Title

ENABLING EFFICIENT UPLINK (RE) TRANSMISSIONS IN AN INTERFERE- CANCELLATION BASED SYSTEM USING NETWORK ASSISTANCE

Field

The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to a method and apparatus for use in a

communication network.

Background

A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations/access points and/or other nodes by providing carriers between the various entities involved in the

communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

In a wireless communication system at least a part of a communication session between at least two stations occurs over a wireless link.

A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The

communication device may access a carrier provided by a station or access point, and transmit and/or receive communications on the carrier. The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. One example of a communications system is UTRAN (3G radio). Other examples of communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology and so-called 5G or New Radio (the term used by 3GPP) networks. Standardization of 5G or New Radio networks is currently under discussion. LTE is being standardized by the 3rd Generation

Partnership Project (3GPP).

One of the requirements that must be taken into consideration in the development of new radio networks is the need to manage interference between signals transmitted from different access points (APs) in the network.

Summary of the invention

According to a first aspect, there is provided a method comprising: receiving information at a second network access point, the information comprising an indication of at least one time period; determining the available resources for transmitting data to a first network access point from the second network access point via a backhaul communication link; and applying a second network access point transmission mode during the at least one time period in dependence upon the determination of the available resources.

In one embodiment, the backhaul communication link is between the first network access point and the second network access point.

In one embodiment, the information received at the second network access point is received from the first network access point.

In one embodiment, the information received at the second network access point is received from a central co-ordinator configured to communicate with the first network access point and the second network access point.

In one embodiment, the information comprises an indication of transmission and reception activity of a first network access point during a plurality of time slots. In one embodiment, the information comprising an indication of at least one time period comprises a request for interference cancellation support during the at least one time period.

In one embodiment, each time period of the at least one time period is a subframe.

In one embodiment, the method further comprises: if it is determined that the available resources exceed a predetermined value, transmitting data indicating at least part of data scheduled for transmission by the second network access point in the at least one time period to the first network access point via the backhaul communication link.

In one embodiment, further comprises: if it is determined that the available resources do not exceed a predetermined value, performing at least one of: transmitting data from the second network access point to one or more user devices during the at least time period, wherein said data is a copy of data previously transmitted by the second network access point; muting transmission of data between the second network access point and the one or more user devices during the at least one time period; and scheduling transmission of data from the one or more user devices to the second network access point during the at least one time period.

In one embodiment, said data previously transmitted is data for which a message was received from said one or more user devices, said message indicating a failed transmission of said data previously transmitted.

In one embodiment, the method further comprises: performing the step of transmitting data from the second network access point to one or more user devices if the data previously transmitted was transmitted within a predefined time period or a predefined number of transmission units prior to the at least one time period.

In one embodiment, the method further comprises: performing the step of transmitting data from the second network access point to one or more user devices in accordance with non- adaptive hybrid automatic repeat request.

In one embodiment, the method further comprises: if the data previously transmitted was not transmitted within a predefined time period or a predefined number of transmission units prior to the at least one time period, performing at least one of the steps of: muting transmission of data between the second network access point and the one or more user devices during t e time period; and scheduling transmission of data from the one or more user devices to the second network access point during the time period.

In one embodiment, the at least one time period comprises periodically occurring time periods.

According to a second aspect, there is provided a computer program product for a computer, comprising software code portions for performing the steps of the first aspect when the product is run on the computer.

According to third aspect, there is a method comprising: transmitting from a first network access point, information to a second network access point, the information comprising an indication of at least one time period; and receiving an indication of a second network access point transmission mode for use during the at least one time period, wherein the transmission mode is selected in dependence upon a determination of the available resources for transmitting data from the second network access point to the first network access point via a backhaul communication link.

In one embodiment, the backhaul communication link is between the first network access point and the second network access point.

In one embodiment, the information comprises an indication of transmission and reception activity of the first network access point during a plurality of time slots.

In one embodiment, the information comprising an indication of at least one time period is a request for interference cancellation during the at least one time period.

In one embodiment, each time period of the at least one time period is a subframe.

In one embodiment, the method further comprises: receiving from the second network access point, an indication of transmission and reception activity of the first network access point during a plurality of time slots; and selecting the at least one time period from the plurality of time slots in dependence upon the indication of transmission and reception activity.

In one embodiment, further comprises: if it is determined that the available resources exceed a predetermined value, receiving data from the second network access point via the backhaul communication link, said data indicating at least part of transmission data scheduled for transmission from the second network access point in the at least one time period; scheduling, during the at least one time period, uplink transmission of data from a user device; and detecting a signal during the at least one time period and using said data indicating at least part of transmission data to reduce interference from a transmission of the second network access point in the signal.

In one embodiment, the method further comprises: storing data from a first signal received during a first time period from the second network access point; scheduling during the at least one time period, uplink transmission of data from a user device; detecting a second signal during the at least one time period; and if it is determined that the available resources do not exceed a predetermined value: correlating the first signal and the second signal to determine that the second signal comprises a copy of data transmitted from an access point during the first time period; and removing interference from the second signal using the correlation between the first signal and the second signal.

In one embodiment, the method of further comprises: scheduling high priority data for uplink transmission from a user device during the at least one time period.

In one embodiment, the method further comprises: scheduling for uplink transmission from a user device during the at least one time period, data which was previously scheduled in a failed uplink transmission.

In one embodiment, the method further comprises: prior to determining the at least one time period, receiving from a network, an indication of a proportion of total time to be comprised by the at least one time period; and determining the indication of the at least one time period in dependence upon the received indication of the proportion of total time.

In one embodiment, the method further comprises: re-scheduling control information for transmission to a user device at a different time period from the at least one time period.

In one embodiment, the method further comprises: transmitting to the user device an indication that the control information will not be transmitted during the at least one time period.

In one embodiment, the indication comprises an indication of a time period in which the control information is re-scheduled for transmission to the user device. In one embodiment, further comprises: transmitting an instruction to a user device to cause the user device to mute transmission of control information during the at least one time period.

According to a fourth aspect, there is provided a computer program product for a computer, comprising software code portions for performing the steps of the third aspect when the product is run on the computer.

According to a fifth aspect, there is provided an apparatus comprising: at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: receive information at a second network access point, the information comprising an indication of at least one time period; determine the available resources for transmitting data to a first network access point from the second network access point via a backhaul communication link; and apply a second network access point transmission mode during the at least one time period in dependence upon the determination of the available resources.

According to a sixth aspect, there is provided an apparatus comprising: at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to: transmit from a first network access point, information to a second network access point, the information comprising an indication of at least one time period; and receive an indication of a second network access point transmission mode for use during the at least one time period, wherein the transmission mode is selected in dependence upon a determination of the available resources for transmitting data from the second network access point to the first network access point via a backhaul communication link.

Brief Description of Drawings

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic diagram of an example communication system comprising a plurality of base stations and a plurality of communication devices;

Figure 2 shows a schematic diagram of an example mobile communication device; Figure 3 shows a schematic diagram of an example communication system comprising two cells, each having a base station and user equipment;

Figure 4 shows two tables, each showing the direction of communication between an access point and user equipment;

Figure 5 shows a schematic diagram of an communication system comprising two access points, two sets of user equipment and a central coordinator;

Figure 6 shows example uplink/downlink patterns for two access points;

Figure 7 illustrates a method performed at an access point to reduce the level of interference produced by transmission from that access point at a neighbouring access point;

Figure 8 illustrates a method performed at an access point to reduce the level of interference produced at that access point by transmissions from a neighbouring access point; and

Figure 9 shows a schematic diagram of an example control apparatus. Detailed Description

Before explaining in detail the examples, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to Figures 1 to 2 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in figure 1 , mobile communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. A base station is referred to as an eNodeB (eNB) in LTE. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatus. The controller apparatus may be part of t e base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

LTE systems may however be considered to have a so-called "flat" architecture, without the provision of RNCs; rather the eNB is in communication with a system architecture evolution gateway (SAE-GW) and a mobility management entity (MME), which entities may also be pooled meaning that a plurality of these nodes may serve a plurality (set) of eNBs. Each UE is served by only one MME and/or S-GW at a time and the (e) NB keeps track of current association. SAE-GW is a "high-level" user plane core network element in LTE, which may consist of the S-GW and the P-GW (serving gateway and packet data network gateway, respectively). The functionalities of the S-GW and P-GW are separated and they are not required to be co-located.

In Figure 1 base stations 106 and 107 are shown as connected to a wider communications network 1 13 via gateway 1 12. A further gateway function may be provided to connect to another network.

The smaller base stations 1 16, 1 18 and 120 may also be connected to the network 1 13, for example by a separate gateway function and/or via the controllers of the macro level stations. The base stations 1 16, 1 18 and 120 may be pico or femto level base stations or the like. In the example, stations 1 16 and 1 18 are connected via a gateway 1 1 1 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided.

A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia, and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2, transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto. The communication devices 102, 104, 105 may access the communication system based on various access techniques.

Reference is now made to figure 3, which provides an illustration of a wireless

communication system 300, which may be used to illustrate one or more problems that may exist with the prior art.

The communication system 300 comprises a first access point 302 and a second access point 304. The access points may be macro level base stations. Alternatively, the access points may be micro, pico, or femto level base stations. The first access point 302 is configured to communicate with a first UE 306, whilst the second access point 304 is configured to communicate with a second UE 308. Both of the access points may be configured to communicate with their respective UE by means of time division duplex (TDD) in which uplink communications from the UE to the access point are allocated different time slots in the same frequency band to downlink communications from the access point to the UE.

Reference is made to figure 4, which show two different TDD patterns that may be employed for communication between a UE and an access point. Figure 4 shows a pattern 402 that may be used for communication between UE 306 and access point 302. Similarly, figure 4 also shows a pattern 404 that may be used for communication between UE 308 and access point 304. The figures show a direction of communication (i.e. uplink or downlink) for each timeslot or 'subframe'. Although the following explanations refer to selecting uplink or downlink for each subframe, it would be appreciated by the person skilled in the art that embodiments are not limited in their application to subframes, but may be applied more generally to timeslots in which portions of data are transmitted. Hence, when, in the following description, reference is made to 'subframes', it should be understood that any timeslot suitable for transmitting a portion of data may be intended.

Figure 4 shows that a first subframe in the pattern 402 is a downlink subframe, at which data is transmitted from the first access point 302 to the UE 306. At the same time, it is shown that at the first subframe in the pattern 404, data is transmitted between the second access point 304 to the UE 308 is also a downlink subframe. Therefore, both access points are transmitting data to their respective UEs at the first subframe. However, at subframe 3 of pattern 402, the communication at the first access point 302 is an uplink transmission, where a subframe is sent from the UE 306 to the first access point 302. At the same time, the subframe 3 of pattern 404, at which data is transmitted from the second access point 304, is a downlink subframe. This transmission of data at the downlink subframe from the second access point 304 may interfere with the data at the uplink subframe received at the first access point 302. For example, the uplink signal received at the first access point 302 from the UE 306 could be -80dBm, whilst the signal received at the first access point 302 from the downlink transmission from the second access point might be -85dBm. Therefore, the uplink subframe received at the first access point 302 may suffer a significant amount of interference, having an SINR of 5 dB, at subframe 3. In this case, the first assess point 302 may be referred to as the victim AP for subframe 3, whilst the second access point 304 may be referred to as the interring AP for subframe 3. Similarly, at subframe 6 of pattern 404, data is transmitted between the second access node 304 and the UE 308, and this subframe is therefore an uplink subframe, whilst at subframe 6 of pattern 402 data is transmitted between the second access node 302 and UE 306, and this subframe is therefore a downlink subframe.

Therefore, the signal from the first access node 302 may interfere with the uplink signal received at the second access node 304. In this case the first assess point 302 may be referred to as t e interfering AP for subframe 6, whilst the second access point 304 may be referred to as the victim AP for subframe 6.

It could be possible to arrange the TDD patterns used by the neighbouring access nodes to avoid the interference which results when one of the access points is operating in the uplink and another is operating in the downlink. However, it may be advantageous to adapt the TDD pattern over time depending upon, for example, whether or not the user predominately wants to transmit up or download data at a particular point in time. This flexible/dynamic TDD can significantly improve network capacity and guarantee efficient resource utilization, since it allows for dynamic utilization of the spectrum for downlink (DL) and uplink (UL), depending on the instantaneous user demands. However, the changes to the patterns can lead to strong interference between neighbouring cells with traffic asymmetries. Strong interference can cause an increase in the transmission failure rate, which will in turn lead to a high amount of uplink re-transmissions via hybrid automatic repeat request (HARQ).

A method typical in 4G is to apply dynamic coordinated blanking (muting) of the transmission of interring APs, however this approach leads to sacrificing throughput of the interring APs. The conventional solutions try to avoid strong interference scenarios with appropriate transmission coordination, e.g. inter-cell interference coordination (ICIC) or coordinated dynamic point muting. Therefore, these solutions generally limit the resource reuse factor. Another approach is to apply interference cancellation (IC). However, one limitation is that the interference has to be decoded and in the case of higher order modulation and coding scheme (MCS) at interferer, the decoding probability could be low.

Thus the inability of a victim AP to effectively cancel (or suppress) the interfering downlink transmission may result in a high decoding failure of uplink transmissions, which will in turn lead to high amount of uplink re-transmissions via hybrid automatic repeat request (HARQ). In cases when the interfering cell has a high amount of downlink transmissions, this may result in unacceptable quality of service in the victim cell.

The HARQ technique is used for retransmission of the failed initial transmissions along with storing the received packet for combining all the received portions of the same packet by a negative-acknowledgment (NACK) message. In HARQ, the receiving node simply informs the transmitter about the decoding failure of the packet and stores the received information for a more efficient future combining with the received retransmissions. The transmitter will transmit extra redundancy of the same packet over the data channel after receiving a NACK from the receiver entity. In any subsequent transmission attempt (so-called retransmission), the receiver will evaluate the received data while considering the earlier information. This way, the receiver combines the old and new data to increase the decoding success chances. HARQ is a well-recognized technique for solving problems with channel fluctuations like fading and interference, since it can increase t e channel utilization efficiency compared to simple ARQ retransmission. On the other hand, since for latency purposes, certain applications may be designed to work without using HARQ. The absence of HARQ (or a long HARQ window) for these applications thus makes network assistance even more important in order to guarantee the required quality-of-service (QoS).

Therefore, there is a need to reduce the interference at a victim AP from an interfering AP during uplink transmission from one or more UEs to the victim AP.

Referring back to figure 3, one way in which this could be achieved is to pass interference data from an interfering AP (e.g. access point 304) to a victim AP (e.g. access point 302) via a backhaul communication link 310, such as X2 signalling via a wired (or wireless) connection or an optical fiber connection. This interference data may comprise DL (downlink) signal information and/or DL data, which the victim AP could use to estimate the inter-AP interference. The estimated inter-AP interference signal can be subtracted from the uplink signal to form an inter-node interference compensated uplink signal. However, there may be problems with this approach, since it may be limited by the backhaul latency needed to constantly transmit the interference data from the interfering AP.

As mentioned above, one approach to reducing interference, would be to mute strongly interfering APs while an uplink transmission is taking place. However, this approach may degrade the performance of the interfering AP that is muted.

Reference is now made to figure 5, which shows a communication system 500 according to embodiments of the application. The system includes a first access point 502 (AP1 ) configured to communicate with a first user equipment 506 (UE1 ) and a second access point 504 (AP2) configured to communication with a second user equipment 508 (UE2). The access points may be macro level base stations. Alternatively, the access points may be micro, pico, or femto level base stations. Both of the access points may be configured to communicate with their respective UE by means of time division duplex (TDD). Although the figure presents only one UE (UE1 ) that communicates with AP1 , and one UE (UE2) that communicates with AP2, it would be understood by the person skilled in the art that each AP may communicate with multiple UEs. Hence, when, in the following description, reference is made to 'UE', it should be understood that a plurality of UEs may covered.

The access points may also be configured to communicate with one another by means of a backhaul communication link 510, such as X2 signalling via a wired (or a wireless) connection or an optical fiber connection. The communication system 500 may additionally include a central co-ordinator that is configured to communicate with both AP1 502 and AP2 504. As noted, it may be possible to perform interference cancellation on a signal received at an AP using data received via a backhaul communication link. However, continually transmitting data needed to cancel the interference can lead to an overload problem since a lot of backhaul capacity will be needed. Instead in embodiments of the application, a certain subframe of data in the transmission of the interfering AP is selected for performing interference cancellation. During this subframe, high priority data may be transmitted on the uplink to the victim AP from the corresponding UE. Additionally or alternatively, data from a previously failed uplink transmission may be retransmitted during this subframe. Therefore, even if a transmission failure results due to interference, the data may be retransmitted at a later point when the interference cancellation is in effect.

The subframes for which interference cancellation is carried out data are referred to as 'known subframes'. The proportion of subframes in the transmissions between the interfering AP and its corresponding UE that are known subframes for which the interference cancellation is carried out using backhauled data may be determined by a central coordinator 512, which is included in the system, in dependence upon the capacity of the backhaul communication link 510. If the backhaul communication link 510 capacity is low, then the proportion of subframes in the transmission between the interfering AP and the corresponding UE that are known subframes will be low. On the other hand, if the backhaul communication link capacity is high, then the proportion of subframes in the transmission between interfering AP and the corresponding UE that are known subframes will be high.

At a known subframe, the interfering AP may enable interference cancellation at the victim AP by providing data via a backhaul communication link to the victim AP. This data may be referred to as a priori data. The victim AP may be configured to use the a priori data to estimate the interference signal that will be received at the victim AP from the interfering AP when the interfering AP transmits data at the known subframe. The victim AP may use this estimate of the interference signal to correct the signal received at the AP during uplink from the UE to produce an interference cancelled signal.

The a priori data may be a copy of the downlink data to be transmitted by the interfering AP to its corresponding UE or may take another form. In one embodiment, the interfering AP may comprises a parallel buffer in which the data to be transmitted at the known subframe is enqueued for transmission via the backhaul communication link to the victim AP and for downlink transmission to the corresponding UE. The copy of the data to be sent to the victim AP is sent to the victim AP a predefined amount of time prior to the occurrence of the known subframe. The copy of the data to be transmitted on the downlink to the UE is sent on the known subframe. The use of the parallel buffer may enable this pre-scheduling of the data so that it may be sent to the victim AP prior to the known subframe. Prior to performing t e interference cancellation, the two APs, AP1 and AP2, may share their UL/DL patterns. This sharing may make use of the backhaul link 510 or alternatively may be made through the central coordinator 512. In some embodiments, the central coordinator may determine UL/DL patterns for both APs and then transmit each UL/DL pattern to each AP. The UL/DL pattern for an AP comprises an indication of transmission and reception activity of a first network access point during a plurality of time slots. This pattern comprises an indication for each subframe as to whether that subframe is an uplink or downlink subframe. The pattern may also indicate if a subframe is flexible, i.e. the AP can determine whether to perform uplink or downlink at that subframe later. In some cases, the pattern may indicate whether or not a subframe is already allocated to be a known subframe. In some cases, AP1 may be configured to analyse and compare the UL/DL pattern of AP2 to its own UL/DL pattern and select one of the subframes in the UL/DL pattern of AP2 to be a known subframe. For example, AP1 may determine an uplink subframe in its own pattern that overlaps in time with a downlink subframe in the pattern of AP2. AP1 may then determine that this subframe in the pattern of AP2 is to be a known subframe, for which interference cancellation may be carried out. AP1 may then inform AP2 of the determined known subframe. AP1 may transmit to AP2 a request for inference cancellation support, the request identifying a subframe (the known subframe) for which interference cancellation is requested to be carried out.

Prior to the transmission of the data of the known subframe from AP2 to UE2, AP2 is configured to transmit via the backhaul communication link 510 the data (a priori data) which enables AP1 to perform the cancellation of the interference resulting from the downlink transmission of the known subframe at AP2.

AP1 may be configured to schedule for uplink transmission from the UE1 , during the known subframe, high priority data. Additionally or alternatively, AP1 may schedule for uplink transmission, data which was unsuccessfully transmitted from UE1 to AP1 in a previous subframe. In accordance with the HARQ mechanism, when the UE1 transmits data to the AP1 , UE1 awaits receipt of an acknowledgment (ACK) from AP1 indicating successful receipt of the data at the AP1 . However, the data may not be successfully received at AP1 , for example, due to interference from the downlink transmission of AP2. In this case, AP1 transmits a negative acknowledgement (NACK) to UE1 , which may then schedule the data for retransmission. The UE1 may be configured to schedule the data for retransmission during the known subframe in response to a request from AP1 .

In one embodiment, if the latency between the central coordinator 512 and the victim AP is less that a predefined value, the central coordinator will make the selection of a subframe to be a known subframe. The central coordinator may then transmit the request to the interfering AP for t e selected subframes to be known subframes and may also transmit an indication of the selection of the known subframes to the victim AP. If the latency is greater than the predefined value, the victim AP may then make the selection of subframes, which are requested to be known subframes. The victim AP may then transmit that request to the interfering AP. However, in this case, the central coordinator 512 may still be configured to determine a quota for the number of known subframes and transmit this indication to the victim AP. The quota providing an indication of the proportion of subframes which may be selected as known subframes. The central coordinator may determine the quota in dependence upon a measurement of the communication resources available for communication between the two access points. The measurement of the communication resources may be the capacity of the backhaul communication link 510. If the capacity is low, the proportion of subframes that are known subframes may be low, whereas if the capacity is high, the proportion of subframes that are known subframes may be high.

Hence, the measurement of the communication resources is used to select a particular transmission mode for the interfering AP for a subframe. One transmission mode may involve the transmission of a priori data via the backhaul communication link 510 to the victim AP. Another transmission mode may involve the transmission of repeat data on the subframe. Another transmission mode may involve muting the interfering AP during the subframe. Another transmission mode may involve switching the activity of the interfering AP from downlink to uplink during the subframe.

In some cases, the capacity of the backhaul communication link 510 may be low. In this case, it may be more challenging to rely on the use of a priori data for performing the interference cancellation since the backhaul communication link 510 may not be capable of transmitting much a priori data. In this case, AP2 may determine whether or not there are any subframes that it previously transmitted in the downlink, for which a re-transmission is required. Similarly to as described above, in accordance with the HARQ mechanism, when the AP2 transmits data to the UE2, AP2 awaits receipt of an acknowledgment (ACK) from UE2 indicating successful receipt of the data at the UE2. However, the data may not be successfully received at UE2, for example, due to interference from the downlink transmission of AP1 . In this case, UE2 transmits a message indicated that the transmission of the data from AP2 has failed. This message may be a negative acknowledgement (NACK) to AP2, which may then schedule the data for retransmission. The AP2 may be configured to schedule the data for retransmission during uplink transmission of data to AP1 from UE1 . The subframe which is re-transmitted by AP2 may be referred to as a repeat subframe. AP1 may store previously received subframes, which it may compare to the data received on the uplink when AP2 transmits the received subframe. AP1 may correlate a signal received from AP2 at a previous subframe with the uplink data to estimate an amount of interference in the uplink data resulting from the re-transmitted subframe. AP1 may then correct the received uplink data to remove the interference using the interference estimate.

AP1 may store the previously received subframes for a predefined amount of time. Alternatively, AP1 may store a predefined number (e.g. 20) of previously received subframes. AP1 may provide to AP2 an indication of the predefined amount of time or predefined number of subframes and AP2 may use this indication to determine a repeat subframe to transmit on the downlink to UE2. If in response to the indication provided by AP1 , AP2 determines that AP1 does not have data stored from a particular previously received subframe, AP2 may determine not to transmit a repeat of the downlink data for that subframe. On the other hand, if, in response to the indication provided by AP1 , AP2 determines that AP1 has data stored from a particular previously received subframe, AP2 may determine to transmit a repeat of the downlink data for that subframe.

The repeat data at the second subframe may be transmitted by AP2 in accordance with non-adaptive HARQ, wherein the transmission attributes such as modulation order, code rate, and the amount of resource allocation of the re-transmitted data at the second subframe are the same as for the originally transmitted data at the first subframe. This causes the interference at AP1 resulting from the re-transmitted data at the second subframe to be similar to the interference resulting from the original transmission at the first subframe, hence enabling cancellation of the interference.

In some embodiments, the identity of the repeat subframes in the UL/DL pattern of AP2 may be predetermined. As will be explained, AP2 and AP1 may be configured to exchange UL/DL patterns. AP1 may therefore receive from AP2, the UL/DL pattern of AP2 and determine from the pattern, the subframes in the pattern at which data for which a failed transmission has already occurred is to be retransmitted.

In some cases, AP2 may not have available any data that is scheduled for re- transmission. This may be because there have been no failures in transmission within a predefined period of time or a predefined number of subframes and hence no NACKs have been received from UE2. In this case, the network may configure AP2 to mute, and not transmit or receive any data from/to UE2 at subframes during the time period. The uplink transmission from UE1 to AP1 , will then be free from interference from AP2.

In another embodiment, in response to determining that AP2 does not have any data that is scheduled for re- transmission, AP2 may be configured for a particular subframe to switch from downlink transmission to uplink, so as to receive data at that subframe from UE2. As noted above, t e interference produced at AP1 from uplink at AP2 is minimal and therefore, for this particular subframe, the interference is significantly reduced.

When downlink data is transmitted from the access point to a UE, it is common for control information to be included in the data. This control information may be in-resource control signalling, for example. However, the a priori data that is transmitted via the backhaul communication link to AP1 (the victim AP) for interference cancellation at a known subframe may not contain this control information. Therefore, at the known subframe, AP2 (the interfering AP) may transmit the downlink data without the control information. However, in this case, the UE2 will need to be informed that the control information will not be sent as part of the downlink data. Therefore, prior to the known subframe, AP2 transmits an indication that the control information for that downlink data will not be sent on the known subframe. The indication may comprise an indication that the downlink data will be sent previous to the known subframe or following the known subframe. The indication may comprise the control information itself. The UE2 may be configured to receive the indication and process the indication so as to prepare for processing the control information at the relevant time point.

In some cases, the UE may send control information to the AP on the uplink at the same subframe at which the AP is transmitting downlink data to the UE. This may be referred at bidirectional uplink control signalling. Prior to a known subframe, AP2 may transmit an instruction to UE2 not to perform the bidirectional uplink control signalling. UE2 may then receive this instruction from UE2 and not perform the bidirectional uplink control signalling at the known subframe. UE2 may instead send the control information that would have been sent at the known subframe, on an earlier or later subframe. Not sending the uplink control information on the known subframe may help AP1 to treat the known subframes similar to an almost blank subframe (ABS) for sending control information.

In one embodiment, the a priori data that is sent via the backhaul communication link may contain the above mentioned control information. In this case, UE1 may be configured to transmit the control information to AP1 at the ABS in one format, and the control information to AP1 at the known subframe in another format.

Reference is now made to figure 6, which shows an example of UL/DL patterns at AP1 and AP2. The label 'UL' indicates that the AP is receiving data at a subframe from a UE. The label 'DL' indicates that the AP is transmitting data at a subframe to a UE.

The label 'KS' refers to a known subframe, which may be the same as a /DL subframe except that the AP will, prior to the transmission of the data to/from the UE in the subframe, share with the victim AP, at least some of the data that will be transmitted in the UL/DL in the subframe. The label 'FX' indicates a subframe that is flexible, i.e. may be either DL or UL. The AP may be able to determine whether a flexible subframe is to be DL or UL in dependence upon the UL/DL pattern of another AP which it receives. It may be determined to make one of the subframes a known subframe so as to allow for interference cancellation at a victim AP. In one embodiment, it may be determined to make one of the flexible subframes a repeating subframe so as to allow for interference cancellation at a victim AP.

The label 'FR' indicates that no transmission activity takes place at the AP, i.e. the subframe is muted.

In some cases, AP1 may transmit a request to AP2 for an identified subframe to be treated as a known subframe i.e. a request for interference cancellation support. The selection of the particular subframe as a known subframe may be a onetime event.

In some cases, AP1 may transmit a request to AP2 for known subframes to occur periodically in the UL/DL pattern of AP2. AP1 may send a request indicating the frequency with which AP2 is to schedule a subframe as a "known subframe". The request may be received at AP2, and may configure AP2 to transmit a priori data via the backhaul communication link to AP1 every nth subframe. Alternatively, AP2 may be configured to mute a subframe every nth subframe.

As noted earlier, in one embodiment, AP1 and AP2 are configured to exchange their UL/DL patterns. This may be performed when the latency of the backhaul communication link is low and the capacity of the backhaul communication link is high. After exchanging UL/DL patterns, AP1 and AP2 may then configure their UL/DL patterns appropriately by, for example, scheduling the transmission of high priority data and data for re-transmission over subframes which are indicated in the neighbouring AP as being 'FR' or known subframe or UL. Priority may be given to one of these types of subframes over another for the transmission of high priority data or re-transmission data. For example, AP1 may prioritise high priority data and data for re-transmission for uplink on a subframe which is indicated in the AP2 pattern as being 'FR'. If no 'FR' is available in the AP2 pattern for the transmission of the particular data, AP1 may then schedule high priority data and data for re-transmission for uplink on a subframe which is indicated in the AP2 pattern as being 'KS'. If no 'KS' subframe is available in the AP2 pattern, then AP1 may then schedule high priority data and data for re-transmission for uplink on a subframe which is indicated in the AP2 pattern as being 'UL'. This order of priority may be selected due to the amount of interference at AP1 during uplink for each subframe at AP2. Specifically, the 'FR' subframe generates less interference at AP1 than results from the 'KS' subframe after interference cancellation, and the 'KS' subframe results in less interference at AP1 after interference cancellation than the 'UL' subframe. In the example, shown in figure 6, AP1 after receiving the UL/DL pattern of AP2, schedules subframe 7 for the re-transmission from the UE1 in the uplink of data that was previously unsuccessfully transmitted. The selection of subframe 7 may be made in response to the determination that subframe 7 in the UL/DL pattern of AP2 is an uplink subframe, and therefore the level of interference at AP1 will be low.

Similarly, subframe 5 in the UL/DL pattern of AP1 could be used for the uplink transmission of high priority data from UE1 . The selection of subframe 5 for high priority data transmission may be made in response to the determination that subframe 5 in the UL/DL pattern of AP2 is an uplink subframe, and therefore the level of interference at AP1 will be low.

Subframe 6 in the UL/DL pattern of AP1 may also be used for the uplink transmission of high priority data or re-transmission of data. The selection of subframe 6 for high priority data transmission or re-transmission may be made in response to the determination that subframe 6 in the UL/DL pattern of AP2 is a known subframe, and therefore AP1 will receive the a priori data from AP2 via the backhaul communication link 510, which it may use to perform interference cancellation on the signal received in the uplink at subframe 6.

AP2 may also be subject during its uplink transmission, to interference from downlink transmission from AP1 (i.e. AP2 it may be a victim AP). Therefore, AP2 may receive the UL/DL pattern of AP1 and make similar determinations so as to reduce interference in the uplink signals.

For example, subframe 9 in the UL/DL pattern of AP2 may be used for the uplink transmission of high priority data from UE2 to AP2. The selection of subframe 9 for high priority transmission may be made in response to the determination that subframe 9 in the UL/DL pattern of AP1 is a known subframe, and therefore AP2 will receive the a priori data from AP1 via the backhaul communication link 510, which it may use to perform interference cancellation on the signal received in the uplink at subframe 9.

However, at subframe 10, it is preferable if AP2 does not schedule high priority data for uplink, since at this subframe, AP1 is transmitting in the downlink without a priori data being received via the backhaul. Therefore, there may be a large amount interference in any uplink signal received at AP2 as a result of the downlink transmission from AP1 , without the possibility of performing interference cancellation from a priori data.

Reference is now made to figure 7, which shows a method that may be performed at an interfering AP. It would understood by the person skilled in the art that an AP may at one point in time be an interfering AP and at another point be a victim AP. In figure 5, the interfering AP could be AP1 at one point in time with AP2 being the victim, and could be AP2 at another point in time with AP1 being the victim. For the purposes of this explanation, AP1 of figure 5 shall be taken to the victim AP, and AP2 shall be taken to the interfering AP. It would be appreciated by the person skilled in the art that not all of the steps of the method are essential to the invention and that one or more of them may be omitted in different embodiments.

At S702, the AP2 receives a request from AP1 for a particular subframe to be treated as a known subframe. AP1 may schedule high priority data to be received on the uplink on this subframe and therefore may make the request in order for signal cancellation to be carried out for that uplink signal.

At S704, AP2 determines whether there exists sufficient communication resources to transmit the a priori data to AP1 . If the data is sent via the backhaul communication link, as in some embodiments, this may involve determining whether or not the capacity of the backhaul communication link 510 would be exceeded by transmitting a priori data via the link 510. This may be performed by determining a value representing the available communication resources for communication between AP1 and AP2. If the value exceeds a predetermined value, then the method proceeds to S706. On the other hand, if it is determined that the value is less than a predetermined value, then the method proceeds to S708. The value may be the available bandwidth associated with the backhaul communication link 510. Alternatively, the value may represent the latency, of the backhaul communication link 510, wherein if the latency is less than a predetermined value then the method proceeds to S706, and if the latency is greater than a predetermined value than the method proceeds to S708.

At S706, AP2 determines that the subframe that was requested to be treated as a known subframe is to be so treated. Prior to this subframe, AP2 is configured to transmit the a priori data via the backhaul communication link 510 so that AP1 may produce an estimate of the interference that will result at AP1 from the data transmitted by AP2 during the known subframe. In other words, AP1 is configured to reconstruct the interfering signal to be received from AP2. The a priori data may comprise at least part of the data to be transmitted by AP2 in the downlink during the known subframe. Following the transmission of the a priori data, AP2 may then perform the downlink transmission by transmitted the data of the known subframe to one or more UEs, such as UE2.

At S708, AP2 determines whether or not there is any data that is available for retransmission. This may be data for which a downlink transmission was previously attempted but which, at least in part, failed. This may be determined by determining whether or not any NACKS have been received for data sent within the last predefined number of downlink subframes. If there is no data available for re-transmission, the method proceeds to S710. On t e other hand, if there is data available for transmission, the method proceeds to S712.

At S710, AP2 is configured to either mute transmission or switch to UL at the subframe which the request from AP1 was received. If AP2 mutes transmission, the downlink data that would have been transmitted from AP2 is no longer transmitted and uplink data is also not received at AP2 for that given subframe. On the other hand, if it is decided to switch to UL, AP2 schedules an uplink transmission from one or more UEs, such as UE2, instead of the downlink transmission.

At S712, it is determined whether it is more beneficial to re-transmit the data in the subframe identified in the request from AP1 or whether it is more beneficial to mute or switch to UL as in S710. If it is determined to be more beneficial to re-transmit the data in the subframe identified in the request from AP1 , the method proceeds to S714. If on the other hand, it is determined to be more beneficial to mute or switch to UL, the method proceeds to S710.

At S714, the AP2 re-transmits a previously transmitted subframe at the subframe identified in the request received from AP1 . The previously transmitted subframe is preferably one containing data that was identified as being unsuccessfully transmitted and which is therefore awaiting re-transmission.

Reference is made to figure 8, which shows a method 800 that may be performed at a victim AP. For the purposes of this explanation, AP1 of figure 5 shall be taken to the victim AP and AP2 shall be taken to the interfering AP. It would be appreciated by the person skilled in the art that not all of the steps of the method are essential to the invention and that one or more of them may be omitted in different embodiments. Furthermore, it should be appreciated that in some embodiments the order in which the steps are performed may differ from the order in which they are presented in method 800.

At S802, AP1 provides a request for a subframe in the UL/DL pattern for AP2 to be a known subframe, i.e. AP1 provides a request for interference cancellation support. AP1 may determine the subframe that is to be selected to be a known subframe by analysing the received UL/DL pattern from AP2. Specifically, AP1 may compare its own UL/DL pattern to that of AP2 and select a subframe which is allocated for downlink by AP2 and which is allocated for uplink by AP1 . AP1 generates a request for the selected subframe to be treated as a known subframe and sends it to AP2. The request may be sent via the backhaul communication link 510. In some embodiments, AP2 may reject the request to treat the identified subframe as a known subframe. However, for the purposes of explanation of the method 800, it is assumed that AP2 accepts the request to treat the subframe as a known subframe and then the method proceeds to S804. In some embodiments, S802 may be omitted as one or more known subframes may already be indicated in the UL/DL pattern of AP2. Hence, a subframe may be treated as a known subframe by AP2 without a request being received from AP1 .

At S804, AP1 schedules for uplink transmission, high priority data or data for retransmission on the subframe. This scheduling may occur by transmitting a message requesting an uplink transmission of the high priority data or re-transmission data to the UE1 prior to the occurrence of the subframe for which the uplink transmission is to be scheduled.

At S806, AP1 determines whether or not the a priori data for the requested known subframe is received over the backhaul communication link 510 from AP2. If such backhaul data is received over the backhaul communication link, then the method proceeds to S808. If, on the other hand, the a priori data is not received, then the method proceeds to S814.

At S808, it is determined whether or not a mute or switch is detected. In some embodiments, AP2 may switch is scheduling for the requested known subframe, from DL to UL (or to mute), for example, to schedule high priority traffic. This switch in the UL/DL pattern at AP2 may be detected at AP1 , via, for example the backhaul communication link 510. If such a switch is detected, the method proceeds to S812. On the other hand, if such a switch is not detected, the method proceeds to S810.

At S810, AP1 uses the a priori data to cancel the interference in the uplink signal that is received from UE1 at the known subframe. This may be achieved by using the a priori data to obtain an estimate of the interference resulting from the AP2 downlink transmission. This resulting estimate may then be subtracted from the detected signal at AP1 during the known subframe to obtain an uplink signal with interference cancellation.

At S812, in response to detecting the switch, AP1 may discard the a priori data. The data may be discarded since interference cancellation is deemed no longer to be necessary, since the interference produced at AP1 , when AP2 is either mute or in the uplink, will be either nil or small.

At S814, the uplink transmission at the requested subframe is performed. AP1 may analyse the received uplink signal and determine whether or not AP2 has broadcast a repeat subframe. AP1 may perform this determination by correlating data that was previously received from AP2 at a known subframe, which it has stored, with the uplink data received at the requested subframe. If there is a correlation indicating a matching interference pattern between the stored interference data and the uplink data received at the requested subframe, AP1 determines that the requested subframe is a repeat subframe. If it is determined that the requested subframe is a repeat subframe, the method proceeds to S816. If, on the other hand, if it is determined that the requested subframe is not a repeat subframe, the method proceeds to S818.

At S816, the interference is cancelled from the repeat subframe. The correlation between the stored interference data and the requested subframe that was determined in S814, is used to estimate the level of interference in the uplink data at the requested subframe. AP1 may then correct the uplink data to remove the interference using the interference estimate.

At S818, the interference cancellation is not carried out.

Embodiments of the application have the advantage of achieving interference cancellation, whilst minimising dependency upon the capacity of the backhaul communication link, and minimising the performance degradation of the interfering AP. By transmitting the a priori data to the victim AP for an identified known subframe, the victim AP may schedule high priority data or data for retransmission on the specific subframe for which interference cancellation is to be carried out. Hence, there is no need to continuously transmit a priori data from the interfering AP to the victim AP, which would place a strong demand on the communication resources. Furthermore, in the event that the communication resources are not sufficient to transfer the a priori data, the interference cancellation may still be carried out by the interfering AP by doing one of transmitting repeat data on the subframe, muting on the subframe, or switching to uplink from downlink at the subframe. Hence, the interference cancellation may be achieved without dependence upon either continually high capacity of the communication resources between the APs or the muting of the interfering AP.

It is noted that whilst embodiments have been described in relation to one example of a standalone LTE network, similar principles maybe applied in relation to other examples of standalone 3G, LTE or 5G networks. It should be noted that other embodiments may be based on other cellular technology other than LTE or on variants of LTE. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

The method may additionally be implemented in a control apparatus as shown in Figure 9. The method may be implemented in a single processor 201 or control apparatus or across more than one processor or control apparatus. Figure 9 shows an example of a control apparatus 900 for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g. a base station, (e) node B, a central unit of a cloud architecture or a node of a core network such as an MME or S-GW, a scheduling entity such as a spectrum management entity, or a server or host. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 900 can be arranged to provide control on communications in the service area of the system. The control apparatus 900 comprises at least one memory 910, at least one data processing unit 920, 930 and an input/output interface 940. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example, the control apparatus 900 or processor 201 can be configured to execute an appropriate software code to provide the control functions. Control functions may comprise receiving information at a second network access point, the information comprising an indication of at least one time period; determining the available resources for transmitting data to a first network access point from the second network access point via a backhaul

communication link; and applying a second network access point transmission mode during the at least one time period in dependence upon the determination of the available resources.

Alternatively, or in addition, control functions may comprise transmitting from a first network access point, information to a second network access point, the information comprising an indication of at least one time period; and receiving an indication of a second network access point transmission mode for use during the at least one time period, wherein the transmission mode is selected in dependence upon a determination of the available resources for transmitting data from the second network access point to the first network access point via a backhaul communication link.

It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities. In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples. Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.