Patent Description:
In a base station system, aka distributed base station system, aka centralized radio access network (C-RAN) of a wireless communication network, radio access network (RAN) processing is conducted by at least two separate units: a radio unit (RU), and a base band unit (BBU). The BBU is connected to the RU via a fronthaul connection. The fronthaul connection may also be called a fronthaul link. The BBU may also be called a Digital Unit (DU). The RU may also be called Remote Radio Unit (RRU). The RU is connected to one or more antennas through which the RU wirelessly communicates with at least one wireless communication device situated in a geographical cell area to which the RU provides wireless communication coverage. The BBU is in its turn connected to other base station systems or base stations, and to a core network of a wireless communication system. The BBU can be centralized and there may be more than one RU connected to each BBU. Traditionally, the BBU performs advanced radio coordination features such as joint detection, joint decoding, coordinated multipoint transmission (CoMP), to increase the spectrum efficiency and network capacity, as well as baseband signal processing, whereas the RU performs radio frequency (RF) processing and transmission/reception of the RF processed signals. However, in some applications, the RU may also perform some of the signal processing normally performed in the BBU, such as Fast Fourier Transformation (FFT).

In future <NUM> deployments of base station systems, the fronthaul connection between BBU and RU will be packet-based, carrying time-sensitive Long Term Evolution (LTE) or New Radio (NR) physical layer data. Furthermore, the fronthaul connection may be realized as a point-to-point link or as a network. Fronthaul connection utilization will fluctuate with the number of wireless communication devices being served. Furthermore, a fronthaul connection may be shared between multiple base station systems. If the base station systems sharing a fronthaul connection are uncoordinated and the fronthaul connection is not dimensioned for simultaneous peak rates, this might lead to unacceptable queueing or packet losses that have detrimental effect over radio performance.

Due to the time sensitivity requirements and high capacity requirements, one straightforward approach for deployment is isolating fronthaul traffic in a fronthaul network. Throughout this disclosure, it is assumed that such a fronthaul network is used exclusively for fronthaul traffic, e.g. traffic originating from e.g. BBUs, RUs, radio heads, timing providers, etc..

In networked fronthaul deployments supporting New Radio - Time Division Duplex (NR-TDD), traffic generated by synchronized nodes will have a periodicity similar to that of the air interface. That is to say, traffic on the fronthaul connection might show a TDD pattern where links of the fronthaul connection essentially are utilized in half-duplex mode even when signals are aggregated.

Ideally, fronthaul networks should be dimensioned such that they do not severely limit peak rates over the air, but still are reasonably utilized during the day. If there is over-dimensioning, Capital Expenses (CAPEX) will be high due to the cost of optical transceivers, switching equipment such as electrical and optical equipment, and fiber e.g. cost of ports and trenching. Additionally, due to demand fluctuation, over-dimensioning might also contribute to higher Operating Expenses (OPEX) when the extra links will be underutilized, due to e.g. power cost and dark fiber rental cost.

Prior art approaches for sharing of fronthaul infrastructure/connections include dimensioning the shared fronthaul connection for peak rate, relying on packet marking / dropping executed by intermediate nodes, e.g. switches of a fronthaul network, enforcing rate limitations in outbound interface of the intermediate nodes (queueing disciplines) among many other, see e. Solutions that depend only on base station system nodes, i.e. BBU and RU, include the coordination of scheduling decisions for each Transmission Time Interval (TTI) between base station system nodes that share the same fronthaul infrastructure. In this scheme, schedulers of such radio nodes would, in coordinated fashion, avoid distributing assignments/grants above a threshold so as not to surpass limitations in the fronthaul links.

Most of the approaches based only on intermediate nodes have the drawback of depending on dropping or delaying packets for certain flows. Packet drops cause unpredictable radio performance degradation, leading to over-the-air retransmissions, i.e. between the RU and its UEs, and may interfere with link adaptation algorithms; for example, drops in fronthaul may cause retransmissions even for very good radio channel conditions. The acceptable delays over the fronthaul connection are very strict, so solutions that depend on traffic shaping are also not viable.

Solutions that rely on coordination of scheduling decisions for each TTI may avoid problems with packet drops and make the fronthaul capacity constraints transparent to the base station system but require a high number of messages passing between the radio nodes. Background art resource allocation in Cloud Radio access network is described in<NPL>. <CIT> describes orchestration of Radio access network comprising remote radio units, base band units and a fronthaul link. There is a need for an improved way of sharing fronthaul connections.

It is an object of the invention to address at least some of the problems and issues outlined above. It is possible to achieve these objects and others by using methods, systems and BBUs as defined in the attached independent claims.

According to one aspect, a method is provided performed by a system related to a wireless communication network comprising a plurality of base station systems, each base station system comprising a BBU and an RU interconnected via a fronthaul connection. The RUs are arranged to transmit wireless signals to, and receive from, wireless communication devices. The method comprises obtaining fronthaul capacity information on transmission capacity of a part of the fronthaul connection that is shared by a first base station system and a second base station system of the plurality of base station systems, and obtaining information on required capacity for transmission and/or reception of wireless signals by the RU of the first base station system and by the RU of the second base station system towards and/or from the wireless communication devices. The method further comprises determining time unit transmission restrictions for the first base station system and for the second base station system based on the obtained fronthaul capacity information and on the obtained information on required capacity, which time unit transmission restrictions results in fronthaul usage below the transmission capacity of the part of the fronthaul connection, and sending information on the determined time unit transmission restrictions for the first base station system to the BBU of the first base station system and information on the determined time unit transmission restrictions for the second base station system to the BBU of the second base station system.

According to another aspect, a method is provided performed by a BBU of a first base station system of a wireless communication network. The first base station system further comprises an RU. The wireless communication network further comprises a second base station system comprising an RU and a BBU. The BBUs and the RUs of each of the first and second base station system are interconnected via a fronthaul connection, which is shared by the first and the second base station system. The method comprises receiving, from a system related to the wireless communication network, information on time unit transmission restrictions for the first base station system, the time unit transmission restrictions being determined based on fronthaul capacity information on the shared fronthaul connection and on information on required capacity for transmission and/or reception of wireless signals by the RU of the first base station system and by the RU of the second base station system. The method further comprises allocating transmission resources according to the information on time unit transmission restrictions, and triggering communication of signals over the allocated transmission resources with wireless communication devices connected to the RU of the first base station system, according to the allocation.

According to another aspect, a system is provided that is operable with a wireless communication network comprising a plurality of base station systems. Each base station system comprises a BBU and an RU interconnected via a fronthaul connection. The RUs are arranged to transmit wireless signals to, and receive from, wireless communication devices. The system comprises a processing circuitry and a memory. Said memory contains instructions executable by said processing circuitry, whereby the system is operative for obtaining fronthaul capacity information on transmission capacity of a part of the fronthaul connection that is shared by a first base station system and a second base station system of the plurality of base station systems, and obtaining information on required capacity for transmission and/or reception of wireless signals by the RU of the first base station system and by the RU of the second base station system towards and/or from the wireless communication devices. The system is further operative for determining time unit transmission restrictions for the first base station system and for the second base station system based on the obtained fronthaul capacity information and on the obtained information on required capacity, which time unit transmission restrictions results in fronthaul usage below the transmission capacity of the part of the fronthaul connection, and sending information on the determined time unit transmission restrictions for the first base station system to the BBU of the first base station system and information on the determined time unit transmission restrictions for the second base station system to the BBU of the second base station system.

According to another aspect, a BBU is provided that is operable in a first base station system of a wireless communication network, the first base station system further comprising an RU. Further, the wireless communication network comprises a second base station system comprising an RU and a BBU. The BBUs and the RUs of each base station system are interconnected via a fronthaul connection. The fronthaul connection is shared by the first and the second base station system. The BBU comprises a processing circuitry and a memory. Said memory contains instructions executable by said processing circuitry, whereby the BBU is operative for receiving, from a system related to the wireless communication network, information on time unit transmission restrictions for the first base station system, the time unit transmission restrictions being determined based on fronthaul capacity information on the shared fronthaul connection and on information on required capacity for transmission and/or reception of wireless signals by the RU of the first base station system and by the RU of the second base station system. The BBU is further operative for allocating transmission resources according to the information on time unit transmission restrictions and for triggering communication of signals over the allocated transmission resources with wireless communication devices connected to the RU of the first base station system, according to the allocation.

According to other aspects, computer programs and carriers are also provided, the details of which will be described in the claims and the detailed description.

Further possible features and benefits of this solution will become apparent from the detailed description below.

Briefly described, a solution is provided to control the transmission of data over a fronthaul connection shared by two or more base station systems. According to an embodiment, this is achieved by a system coordinating transmission over the shared fronthaul for the base station systems sharing the fronthaul connection. The system obtains information on transmission capacity on the shared fronthaul and obtains information on required capacity for communication of wireless signals by the RUs of the base station systems sharing fronthaul connection. Based on this information the system determines any necessary transmission restrictions on the base station systems and communicates any necessary transmission restrictions, to schedulers of the BBUs of the involved base station systems. The BBUs then allocate transmission resources according to their respective restriction, and possibly also to according to a harmonized transmission scheme for avoiding interference. Hereby, dynamic sharing of fronthaul resources is achieved with low message exchange between the involved base station systems, and also it is not necessary to keep track of fronthaul state in the schedulers.

<FIG> illustrates a wireless communication network in which the present invention may be used. The wireless communication network comprises a first base station system <NUM>, which comprises a BBU <NUM> and an RU <NUM>. The BBU <NUM> has connections to other base station nodes or other radio access network (RAN) nodes and further to a core network so that the distributed base station system can communicate to other nodes of the communication network. The BBU <NUM> is connected with the RU <NUM> via a fronthaul connection <NUM>. The fronthaul connection <NUM> may be any kind of connection, such as a dedicated wireline or wireless connection or a network connection, e.g. an Ethernet network. The RU <NUM> further has at least one antenna <NUM> through which wireless signals are communicated towards and from one or more wireless communication devices <NUM>. The wireless signals comprise data to be communicated from or to the wireless communication devices <NUM>. The wireless communication network further comprises a second base station <NUM>, which also comprises a BBU <NUM> and an RU <NUM>, which has the same function as described above for the BBU <NUM> and the RU <NUM> of the first base station system <NUM>. The BBU <NUM> and the RU <NUM> of the second base station system <NUM> are interconnected via the same fronthaul connection <NUM> as the first base station system <NUM>. In other words, the fronthaul connection <NUM> is shared between the first and second base station system <NUM>, <NUM>. Further, there is provided a system <NUM> that coordinates the usage of the shared fronthaul connection between the first and the second base station system. There may be more than two base station systems that share a fronthaul connection and the system may coordinate usage of the shared fronthaul connection for more than two base station systems. The system <NUM> is connected to the BBU <NUM>, <NUM> of the respective first and second base station system <NUM>, <NUM>.

Further, the RU <NUM> of the first base station system <NUM> provides radio communication coverage to wireless communication devices <NUM> situated within a first geographical cell area <NUM>. In a similar way, the RU <NUM> of the second base station system <NUM> provides radio communication coverage to wireless communication devices <NUM> situated within a second geographical cell area <NUM>, by sending and receiving wireless signals from and to its antenna(s) <NUM>.

The wireless communication network in which the first and second base station systems <NUM>, <NUM> are situated may be any kind of wireless communication network that can provide radio access to wireless communication devices. Example of such wireless communication networks are Long Term Evolution (LTE), LTE Advanced, as well as fifth generation wireless communication networks based on technology such as New Radio (NR).

The wireless communication devices <NUM>, <NUM> may be any type of device capable of wirelessly communicating with an RU <NUM>, <NUM> using radio signals. For example, the wireless communication device <NUM>, <NUM> may be a User Equipment (UE), a machine type UE or a UE capable of machine to machine (M2M) communication, a sensor, a tablet, a mobile terminal, a smart phone, a laptop embedded equipped (LEE), a laptop mounted equipment (LME), a USB dongle, a Customer Premises Equipment (CPE) etc..

<FIG>, in conjunction with <FIG>, describes a method performed by a system <NUM> related to a wireless communication network comprising a plurality of base station systems <NUM>, <NUM>, each base station system comprising a BBU <NUM>, <NUM> and an RU <NUM>, <NUM> interconnected via a fronthaul connection. The RUs <NUM>, <NUM> are arranged to transmit wireless signals to, and receive from, wireless communication devices <NUM>, <NUM>. The method comprises obtaining <NUM> fronthaul capacity information on transmission capacity of a part of the fronthaul connection <NUM> that is shared by a first base station system <NUM> and a second base station system <NUM> of the plurality of base station systems, and obtaining <NUM> information on required capacity for transmission and/or reception of wireless signals by the RU <NUM> of the first base station system <NUM> and by the RU <NUM> of the second base station system <NUM> towards and/or from the wireless communication devices <NUM>, <NUM>. The method further comprises determining <NUM> time unit transmission restrictions for the first base station system <NUM> and for the second base station system <NUM> based on the obtained <NUM> fronthaul capacity information and on the obtained <NUM> information on required capacity, which time unit transmission restrictions results in fronthaul usage below the transmission capacity of the part of the fronthaul connection, and sending <NUM> information on the determined time unit transmission restrictions for the first base station system to the BBU of the first base station system and information on the determined time unit transmission restrictions for the second base station system to the BBU of the second base station system.

The system performing the method described in <FIG> may be called a fronthaul controller. The system could be situated anywhere inside or outside the wireless communication network. According to one embodiment, the system is situated close to any of the BBUs, or even in one of the BBUs in order to be able to perform fast instructions. Alternatively, the system performing the method may be a group of network nodes, wherein functionality for performing the method are spread out over different physical, or virtual, nodes of the network, a so called cloud-solution. That the first and second base station systems <NUM>, <NUM> share at least a part of the fronthaul connection signifies that signals between the BBU and the RU of the base station systems are sent at least partly over the same fronthaul connection. The obtained information could be configuration information stored in the system, e.g. since the wireless communication network was last configured. Alternatively, it could be information that the system obtains from another node, e.g. of the wireless communication network. The part of the fronthaul connection that is shared may be the whole fronthaul connection or only a part of it. The term "time unit transmission restrictions" may also be called "time unit transmission resource restrictions" in order to point out that it deals with restrictions for using time unit transmission resources. The time unit transmission resources may be time slots or symbols of time slots, e.g. in a transmission scheme for wireless transmission of signals. In the embodiment where the time unit transmission resources are time slots, the time unit transmission restrictions may be called slot format restrictions. The transmission scheme used may be Time division duplex (TDD) or half-duplex frequency division duplex (FDD) for transmission over the air between the RU and the UEs. The time unit transmission restrictions may be the same or different for the first base station system and the second base station system. The information on determined time unit transmission restrictions are sent to a scheduler of the respective BBU. In case the system that performs the method is situated in one of the BBUs, the information regarding this BBU is sent internally in this BBU from its system to its scheduler.

The scheduler of the respective BBU then refrains from including any downlink (DL) transmissions in the DL time units that are restricted. For uplink (UL) transmissions, according to one embodiment, it is beneficial but not mandatory that the RU is instructed by the system, possibly via the scheduler of the same base station system, to NOT send any UL data in the restricted UL time units back to the BBU, since the scheduler has no use for them and since the FH resources are saved. Further, according to another embodiment, the BBU would not send any scheduling grants towards the RU for the uplink (UL) time units that are restricted.

The time unit transmission restrictions may comprise information for each time unit whether it can be used for sending data or not. Alternatively, the time unit transmission restrictions only comprise information for which time units no data is to be sent. Still alternatively, the information may be for each time unit, e.g. whether the time unit is scheduled as an UL time unit, a DL time unit or a time unit in which no data is to be sent.

Hereby, an efficient way is provided for optimizing utilization of a fronthaul connection that is shared between two or more base station systems. Further, the embodiment can be implemented without needing to introduce awareness of fronthaul constraints into the scheduling entity of each BBU. Instead such awareness only needs to be introduced into the system performing this method. Once the time unit transmission restrictions have been determined and sent to each BBU, the scheduler of each BBU can operate as usual, within those restrictions. Further, the proposed method can be implemented in regular NR signaling, i.e. control channels and interfaces, to enable coordination between base station systems sharing a fronthaul connection. Also, once a feasible combination of slot format restrictions for involved base station systems is defined, the slot format restrictions can be fine-tuned to track parameters such as cell resource utilization, giving fronthaul resources to base station systems according to need.

According to an embodiment, the determined <NUM> time unit transmission restrictions comprises a first mask defining at which time units no data is to be sent between the BBU <NUM> of the first base station system <NUM> and its RU <NUM> and a second mask defining at which time units no data is to be sent between the BBU <NUM> of the second base station system <NUM> and its RU <NUM>. Further, the information sent <NUM> to the BBU <NUM> of the first base station system <NUM> is the first mask and the information sent to the BBU <NUM> of the second base station system <NUM> is the second mask.

By determining such masks defining time units when no data is to be sent, based on required transmission capacity and fronthaul capacity, the amount of data sent can be controlled to be below the fronthaul capacity. Also, by determining such masks, the masks could be overlaid onto already existing harmonized transmission schemes for uplink and downlink transmission so that the limited transmission fits well with the harmonized transmission schemes.

According to another embodiment, the method further comprises, for time units that are configured as uplink time units: initiating sending of the determined time unit transmission restrictions for the first base station system to the RU <NUM> of the first base station system <NUM>, and initiating sending of the determined time unit transmission restrictions for the second base station system to the RU <NUM> of the second base station system <NUM>. By sending the time unit transmission restrictions to the RUs regarding the restrictions that have influence on time units that are configured into UL time units, the RU can act on such transmission restrictions and not send any data in the uplink direction towards its BBU during the uplink time resource that has a restriction.

According to another embodiment, the time unit transmission restrictions defines for which uplink time units no grants are to be distributed by the BBU <NUM> of the first base station system <NUM> towards its RU <NUM> and for which uplink time units no grants are to be distributed by the BBU <NUM> of the second base station system <NUM> towards its RU <NUM>. A grant, aka scheduling grant, is a permission for a UE to transmit at a certain time unit. In this embodiment, the system instructs the BBU not to send any grants to its UEs regarding the uplink time units that are restricted. Hereby, there will be no data sent in the uplink by the UEs in the restricted time units.

According to another embodiment, the time unit transmission restrictions for the first base stations system <NUM> and the time unit transmission restrictions for the second base station system <NUM> are mutually distributed so that available transmission resources for the first base station system and available transmission resources for the second base station system are proportional to the required capacity for transmission and/or reception of wireless signals by the first base station system <NUM> and the required capacity for transmission and/or reception of wireless signals by the second base station system <NUM>. Hereby, a fairness of transmission restrictions are achieved between the base station systems sharing a fronthaul connection.

According to another embodiment, the method further comprises: obtaining <NUM> information on utilization of transmission resources of the first base station system and information on utilization of transmission resources of the second base station system when the determined time unit restrictions of the first and the second base station system are used. the method further comprises adapting <NUM> the determined <NUM> time unit transmission restrictions of the first base station system and the time unit transmission restrictions of the second base station system to the obtained <NUM> information on utilization of transmission resources of the first base station system and information on utilization of transmission resources of the second base station system, and sending <NUM> information on the respective adapted time unit transmission restriction to the respective one of the first and the second base station system. Hereby, an improved usage of the existing transmission resources is achieved, as the usage is adapted to the current situation. The obtaining of information of utilization and the adapting of time unit restrictions may be performed periodically or when triggered, such as when utilization of the transmission resources drops, e.g. below a threshold. The obtaining of information of utilization can be determined by each base station system separately and reported to the system related to the wireless communication network.

According to another embodiment, also a third base station system shares the part of the fronthaul connection <NUM>. Further, the first and the second base station systems <NUM>, <NUM> communicate over a first carrier frequency band and the third base station system communicate over a second carrier frequency band that is different from the first carrier frequency band. Also, the method further comprises instructing <NUM> the third base station system to communicate signals with its wireless communication devices in the same time units as signals are communicated by the first base station system or the second base station system but in an opposite direction as a direction in which the signals are communicated by the first base station system or the second base station system. Signals of the third base station system can coexist with signals of the first and second base station system as they use another frequency and therefore different transmission resources as the first and second base stations. "An opposite direction as a direction in which the signals are communicated by the first base station system and the second base station system" means that it the first or second base station system is sending signals downlink in a time unit, the third base station system sends signals uplink in the same time unit.

<FIG>, in conjunction with <FIG> describes a method performed by a BBU <NUM> of a first base station system <NUM> of a wireless communication network. The first base station system <NUM> further comprises an RU <NUM>. The wireless communication network further comprises a second base station system <NUM> comprising an RU and a BBU. The BBUs and the RUs of each of the first and second base station system are interconnected via a fronthaul connection <NUM>, which is shared by the first and the second base station system <NUM>, <NUM>. The method comprises receiving <NUM>, from a system <NUM> related to the wireless communication network, information on time unit transmission restrictions for the first base station system <NUM>, the time unit transmission restrictions being determined based on fronthaul capacity information on the shared fronthaul connection and on information on required capacity for transmission and/or reception of wireless signals by the RU <NUM> of the first base station system <NUM> and by the RU <NUM> of the second base station system <NUM>. The method further comprises allocating <NUM> transmission resources according to the information on time unit transmission restrictions, and triggering <NUM> communication of signals over the allocated transmission resources with wireless communication devices <NUM> connected to the RU of the first base station system <NUM>, according to the allocation. Hereby, the BBU, especially a scheduler of the BBU just needs to follow received time unit transmission restrictions and does not need to have control itself of any fronthaul capacity limitations and does not have to coordinate usage of such resources with other base station systems sharing the fronthaul connection.

According to an embodiment, the information on time unit transmission restrictions comprises a first mask defining at which time units no data is to be sent between the BBU <NUM> of the first base station system <NUM> and its RU <NUM>.

According to another embodiment, the received information on time unit transmission restrictions defines for which time units no grants are to be distributed by the BBU <NUM> of the first base station system <NUM> towards its RU <NUM>.

According to another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a certain time unit, the method further comprises: reconfiguring downlink transmission resources in that certain time unit into uplink transmission resources, and triggering sending of information on the reconfiguration towards wireless communication devices <NUM> connected to the RU <NUM> of the first base station system <NUM>. Hereby, the wireless communication devices would not unnecessarily check the PDCCH, and thereby battery power is saved at the wireless communication devices. Also, such reconfiguration can be allowed to contradict transmission scheme requirements in TDD-base systems such as Orthogonal Frequency Division Multiplexing, OFDM, as the time units are anyhow not used for any sending as there are transmission restrictions in that time unit.

According to another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a particular time unit, which time unit is set as downlink, the method further comprises reconfiguring a discontinuous reception, DRX, cycle for wireless communication devices <NUM> connected to the RU <NUM> so that the wireless communication devices <NUM> are informed that no signals are to be received at that particular time unit, and triggering sending of information on the reconfiguring to the wireless communication devices <NUM>. As the wireless communication devices <NUM> can stay idle/asleep during that certain time unit thanks to the information on the reconfiguring, battery power of the wireless communication devices <NUM> is saved.

According to yet another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a given time unit, which time unit is set as downlink, the method further comprises sending information on the time unit transmission restrictions for the given time unit to another base station that is not using the shared fronthaul connection. Hereby it is possible for a base station providing coverage to a neighboring cell but does not use the shared fronthaul connection to exploit such a given time unit over the air interface that is not used by the first base station. In other words, a radio resource that is not used due to the limitation in fronthaul can be used by another base station. For example, pilot signals with low interference can be sent by the neighboring base station in the given time unit towards its connected wireless communication devices.

According to yet another embodiment, the method further comprises obtaining <NUM> information on utilization of the allocated transmission resources, sending <NUM> the information on utilization of allocated transmission resources to the system <NUM> related to the wireless communication network, and receiving <NUM>, from the system <NUM> related to the wireless communication network, information on adapted time unit transmission restrictions, in response to the sending <NUM> of the information on utilization. The method further comprises re-allocating <NUM> transmission resources according to the information on adapted time unit transmission restrictions, and triggering <NUM> communication of signals over the re-allocated transmission resources with wireless communication devices <NUM> connected to the RU of the first base station system <NUM>, according to the re-allocation.

According to still another embodiment, the allocating <NUM> of transmission resources according to the information on time unit transmission restrictions comprises translating the time unit transmission restrictions into downlink or uplink formats for the respective transmission resource. In other words, the transmission resources should be set to UL or DL or possibly flexible, even if the transmission resource is not to be used according to the restrictions, this in order to be communication technology-compliant, e.g. NR or LTE compliant, as there are no "blanks" in NR or LTE.

In the following, different embodiments of the invention are described. These embodiments relate to radio access networks using packet-based fronthaul, where the utilization of the fronthaul connections is proportional to that of the air interface, i.e. between the RU and its wireless communication devices. An example of such a radio access network is a network based on O-RAN, see "Control, User and Synchronization Plane Specification, ORAN-WG4. <NUM>", from O-RAN Fronthaul Working Group, March <NUM>. The embodiments assume independent baseband and radio processing units, such as BBUs, and RUs. Each node in a BBU-RU pair executes a subset of RAN physical layer functions for at least one cell. <FIG>, as well as <FIG>, show non-limiting examples of possible fronthaul networking topologies in which the embodiments can be used. <FIG> depicts a daisy-chain topology, where a BBU <NUM> is connected to a first RU <NUM> that in its turn is connected to a second RU <NUM> and so on towards an mth RU <NUM>. In such a topology, the interface <NUM> between the BBU <NUM> and the first RU <NUM> is shared by all m RUs <NUM>, <NUM>, <NUM>. <FIG> depicts a dumbbell-like topology where multiple BBUs <NUM>, <NUM>, <NUM> are connected to multiple RUs <NUM>, <NUM>, <NUM> via intermediate switching nodes <NUM>, <NUM>. The intermediate switching nodes <NUM>, <NUM> may be part of a fronthaul network <NUM> that is shared for communication between the RUs <NUM>, <NUM>, <NUM> and the BBUs <NUM>, <NUM>, <NUM>. The dashed line between the intermediate switching nodes <NUM>, <NUM> represents a logical connection between nodes. The number of hops and nodes of the fronthaul network is not limited to what is shown in <FIG>.

In these embodiments it is assumed that the radio access technology in use is NR and that the duplexing scheme is TDD or half-duplex FDD. As a consequence of this duplexing choice, the fronthaul traffic will also have TDD-like behavior, which means an alternating high- and low utilization pattern tied to the transmit direction in the air interface.

Considering traffic from a single cell, i.e. an RU providing radio coverage to a geographical area, prior to the start of a downlink OFDM symbol transmission, most fronthaul user plane packets will be flowing from BBU to RU nodes, while after the start of an uplink symbol, most user plane packets will be flowing from RU to BBU nodes. This happens because radio base stations connected to the same fronthaul connection should be synchronized to prevent inter-cell interference and connection drops during handover, among other requirements. The synchronization may be achieved through e.g. Precision Time Protocol (PTP).

The method proposed in these embodiments is based on the coordinated utilization of NR slot formats between cells that share a fronthaul connection. If cell A and cell B (see <NUM> and <NUM> of <FIG>) "share" a fronthaul connection, traffic between nodes that implement PHY layer functionality for cell A (RU <NUM> and BBU <NUM> of <FIG>) and traffic between nodes that implement PHY layer functionality for cell B (RU <NUM> and BBU <NUM>) traverse said fronthaul connection.

In the next sections, embodiments of the invention are described, starting with the simplest way to coordinate slot format configuration, and work up to the full mechanism. But before doing that, slot formats and notations used in NR today, i.e. at the air interface, will be described and how they are used in this embodiment.

In NR, OFDM symbols in a slot can be designated downlink (d), uplink (u) or flexible (f). These classes are used to inform the UEs, for example, about when they can transmit and when they might receive scheduling grants and other control information from the gNodeBs they are connected to. Slot formats are <NUM> symbol sequences (e.g. dddd. uuu) defining to which class each OFDM symbol in a slot belongs. Slot formats can be concatenated to form longer sequences specifying how consecutive slots are shared between transmit directions. In this embodiment, upper-case symbols (e.g. D, U, F, S) are used to indicate types of slot formats, i.e. what combination of OFDM symbol types a slot format contains. D (mostly downlink) is used to indicate a slot with at least one downlink and zero or more flexible symbols. Some examples include slot format types <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> as shown in 3GPP TS <NUM> V15. <NUM>, Section <NUM>, Table <NUM>. <NUM>-<NUM> [<NUM>]. U (mostly uplink) is used to indicate a slot with at least one uplink and zero or more flexible symbols. Some examples include slot format types <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in [<NUM>]. F (flexible) is used to indicate a slot with only flexible symbols. Some examples include slot format type <NUM> in [<NUM>]. S (switch) is used to indicate a slot with at least one downlink, at least one uplink and zero or more flexible symbols. Some examples include slot format types <NUM>, <NUM>,. , <NUM> in [<NUM>]. Slot configuration procedures, including slot format tables are described in 3GPP TS <NUM> V15. <NUM>, Section <NUM>, pp. <NUM>-<NUM>, and RRC messages related to slot format configuration are described in 3GPP TS <NUM> V15. <NUM>-<NUM>.

In order to avoid severe interference problems, RUs that are geographically close and use the same frequency band, or bands that overlap at least partly, may be configured in such a way that uplink and downlink transmissions do not occur simultaneously. This restriction may also be necessary, for example, because of coexistence requirements between NR and some other TDD technology. Coordination of slot format choices is a possible solution to surpass this problem. This is shown in "<NPL>.

In the following, and according to embodiments, fronthaul sharing via restrictions of slot formats described above will be described. Suppose that a group of r base station system pairs share a fronthaul connection and implement the PHY layer functionality for cells Ai, with i = <NUM>,. Each of the Ai cells occupies carrier frequency Fca. It is reasonable to assume that due to interference management concerns, the slot formats for each of the Ai cells need to be harmonized, which means that simultaneous downlink-uplink transmissions shall not occur. For the sake of illustration, suppose that a harmonized transmission scheme consists of <NUM> slots that follow the sequence DDDUU. A harmonized transmission scheme can be defined as a restriction on slot formats imposed due to over-the-air coexistence and interference management requirements. Embodiments of this invention comprises restricting portions of the slot format sequence of the harmonized transmission scheme to be used by a subset of the Ai cells in such a way that the aggregate of their fronthaul traffic is below a shared fronthaul connection capacity, while still respecting the harmonized transmission scheme.

An example of slot format restrictions of a harmonized transmission scheme is depicted in Table <NUM> below. Here it is assumed that nodes implementing cell A<NUM> and cell A<NUM> use the same carrier frequency Fca and share same part of a fronthaul network. Further, for dimensioning, the fronthaul network should be capable of sustaining <NUM>% of peak cell throughput in both cells. In this case, the nodes implementing cells A<NUM> and A<NUM> are instructed to avoid each other in their fronthaul usage, while still maintaining compatibility to the harmonized transmission scheme over the air.

Symbol D represents a downlink slot and symbol U represents an uplink slot. Symbol B represents a slot where cell Ai does not distribute assignments or grants. The restrictions in Table <NUM>, i.e. the B-symbols, may be communicated via an Operation and Maintenance (OAM) channel between a fronthaul controller and the nodes implementing cell Ai. If the harmonized transmission scheme and restriction masks of Table <NUM> are used for the network of <FIG>, i.e. if cell <NUM> in <FIG> is cell A<NUM> in table <NUM> and cell <NUM> in <FIG> is cell A<NUM> in table <NUM>, the first base station system <NUM> is assigned restriction mask DBBUB, and the second base station system <NUM> is assigned BDDBU. Hereby, only one base station at a time uses the shared fronthaul link and therefore maximum capacity of the fronthaul link is not exceeded.

<FIG> describes an embodiment of a method for optimizing usage of a shared fronthaul connection. A fronthaul controller obtains <NUM> fronthaul network topology information, including fronthaul capacity information of links of the fronthaul network connecting nodes of the fronthaul network, and possibly also a graph of the fronthaul network including its nodes and links, and routing information. The fronthaul network topology information may be made available to the fronthaul controller by a network management system. The fronthaul controller may be the system <NUM> shown in <FIG>. The fronthaul controller further obtains <NUM> configuration information for each cell, i.e. base station system that shares the fronthaul network, or at least a link of the fronthaul network. The cell configuration information comprises information on required capacity for transmission and/or reception of wireless signals at the RU of each cell, such as information that can be used to determine peak air interface usage for a cell, such as bandwidth, carrier frequency, highest modulation order, harmonized transmission scheme requirements, maximum number of user layers, e.g. Multiple Input Multiple Output (MIMO) layers. From that peak, fronthaul usage for this cell can be determined. Alternatively, the fronthaul controller obtains a value on required capacity for UE communication for each cell directly. Based on the fronthaul network topology information and the configuration information for each cell, the fronthaul controller determines <NUM> a set of slot format restrictions for each cell involved, which restrictions results in a fronthaul usage below each fronthaul link's maximum capacity. The fronthaul controller thereafter signals the determined slot format restrictions to relevant nodes of each cell. The slot format restrictions may be signaled via existing OAM communication interfaces.

As mentioned, each cell is managed by a base station system comprising a BBU and an RU. The slot format restrictions for each cell signaled by the fronthaul controller are received in each respective BBU. The BBU of the cell that the slot format restriction concerns implement the restriction by modifying the cell slot format configuration according to the harmonized transmission scheme with the slot format restrictions. In other words, the BBU of each cell sets <NUM> slot format configuration and allocates radio resources according to the slot format restrictions. For example, when the fronthaul controller as slot format restrictions sends restriction masks such as the restriction masks shown in Table <NUM>, the respective BBU modifies its respective slot formats and allocate radio resources to conform to blank slots B of the respective restriction mask. Observe that a restriction mask may also be on symbol level, i.e. so that a number of symbols of a slot are to be blank (b) but other symbols of the slot can be used for uplink or downlink communication (u or d) according to the harmonized transmission scheme.

The slot format restrictions may be updated, due to changes in network topology, radio equipment changes, changes in interference management requirements, cell usage statistics, quality of Service (QoS) requirements, etc. For this reason, the fronthaul controller checks <NUM> whether the slot formats need to be updated, and if so the method above is repeated.

The fronthaul controller mentioned above can be implemented as a node or set of nodes or a network function. The fronthaul controller can communicate the slot format restrictions with nodes implementing the target cells Ai, e.g. BBUs, using appropriate interfaces such as the Xn, F1 and E1 interfaces, or control plane messages in relevant fronthaul interfaces such as O-RAN and enhanced Common Public Radio Interface (eCPRI).

The output of step <NUM> is, according to an embodiment, a set of slot format usage restriction masks, whose purpose is the signaling of "blanking" periods during which grants and assignments is not to be distributed by cell Ai. Based on the slot format definitions in 3GPP TS <NUM> V15. <NUM>, Section <NUM>, pp. <NUM>-<NUM> [<NUM>], the slot format usage restriction masks can be defined with symbol granularity. A blanking period of one OFDM symbol is denoted by a "b", while a full blank slot, i.e. <NUM> consecutive OFDM symbols, is denoted with "B". As an example, the restriction mask dddbbbbbbbbbbb consists of three downlink symbols followed by eleven symbols over which assignments shall not be distributed. The primary purpose of a slot format restriction mask is to control fronthaul resource utilization. The blanking periods signaled by the mask do not impose a transmit direction over the air. A few examples of slot formats that can be combined with the mask dddbbbbbbbbbbb are presented in Table <NUM>. In Table <NUM>, "sf" stands for slot format. Further, the sf-numbers mentioned refers to reference [<NUM>] above. The combination of transmission scheme, i.e. slot formats before the mask has been set, and mask determine over which scheduling procedure the blanking restriction will be active. In other words, if a blanking period coincides with a "d" symbol, assignments should not occur in that symbol. If they coincide with a "u", grants should not occupy that symbol. If a "b" and an "f" (i.e. flexible symbol) coincide, the "f" symbol shall be silent.

Slot format restriction masks may be defined with symbol granularity, slot granularity or a combination of both. Strings of concatenated masks may be produced, to cover the desired periodicity of the implementation. It should be clear to one skilled in the art that the masks may have multiple efficient representations, such as e.g. bit fields, and that the one disclosed here is chosen for clarity of exposition.

In the following, embodiments for calculating initial slot format restrictions are shown. For a given time granularity, e.g. symbols or slots, the initial restriction masks due to link / can be obtained as follows:.

According to an embodiment, the slot format restrictions may be updated over time. After an initial feasible set of slot format restriction masks has been distributed, the cells are allowed to operate, scheduling radio resources that respect slot format usage masks. In order to avoid suboptimal operation, the slot format restrictions may be updated, e.g. periodically, see step <NUM> of <FIG>. One particular advantageous choice is to monitor the utilization of time-frequency resources of each of the Ai cells. The cells with high utilization can then be prioritized. The utilization can be measured, for example, by the ratio of scheduled to schedulable resource blocks over a certain time interval for each cell. The update can be executed at a suitable rate, or based on defined thresholds. The update can be driven by live metrics collected by a subset of the nodes, e.g. BBUs. These metrics could either be reported to or queried by the fronthaul controller.

According to another embodiment, transmissions from non-interfering cell groups can be multiplexed over the fronthaul connection. Suppose that in addition to the group of cells Ai the target fronthaul deployment supports a second set of cells Ej, j = <NUM>,. , q, with each cell Ej occupying carrier frequency Fce, which is different from carrier frequency Fca occupied by cells Ai. The slot formats for cells in the E group need to be harmonized, but not necessarily between groups A and E as they use different carrier frequencies. That is to say, if A and E are multiplexed in frequency over the air, their fronthaul usage in opposite transmit directions can be simultaneous. If non-interfering groups of cells are present, the fronthaul controller can take advantage of that to allow full duplex operation over the common fronthaul connection.

According to another embodiment, blanking periods, i.e. slots or symbols, may be exploited. As mentioned, when cell Ai's slot format usage is restricted for a time period, e.g. a symbol or more, due to fronthaul limitations, grants and assignments shall not be placed in that time period. Such time periods, i.e. blanking periods (B) can be used by cell Ai's implementing nodes in different ways.

According to a first alternative, if the slot format restriction mask imposes a blank period, said blank period can be configured, e.g. over the air, as either downlink, flexible or uplink, using traditional Radio Resource Control (RRC) interfaces, without violation of the harmonized transmission scheme. In other words, conditioned on some actions, the slot format configuration over-the-air can contradict the harmonized transmission scheme requirement during the blanking period without causing extra interference since there will be no transmission occupying the blank. For example, if a slot is marked as downlink in the harmonized transmission scheme, a blanking cell can configure that interval as uplink as long as it restricts opportunities for random access during the blank. That releases UEs from the need to check the Physical Downlink Control Channel (PDCCH) for control information, resulting in battery savings at the UEs.

According to a second alternative, if a blank is imposed in conjunction with a downlink or flexible symbol in the harmonized slot transmission scheme, the cell can:.

According to a third alternative, if a blank is imposed in uplink, the cell can choose to restrict opportunities for random access and allow for energy savings in its implementing nodes, i.e. in the RU and/or the BBU.

In the following, an example will be described to illustrate proposed embodiments. Consider a fronthaul network shared by cells A<NUM>, A<NUM> and A<NUM>, implemented by BBU-RU pairs. For the purposes of this example, the network can be abstracted as a simple dumbbell topology, with a single link between two switches being the only path between BBU nodes on one side and RU nodes on the other side of the bottleneck, as in <FIG>. As a result of cell planning and neighboring base stations, the harmonized transmission scheme is DDDUU. A usual rule of thumb to dimension the fronthaul network is to provision half of the simultaneous peak rate, i.e. <NUM> * sum of peak demand from cells sharing the fronthaul network. Adding some numbers to the example, consider the bottleneck link dimensioning as: C = (<NUM> * <NUM> no. of cells * <NUM> layers * <NUM> RBs per layer * <NUM> subcarriers per RB * <NUM> bits per <NUM> QAM constellation index * <NUM> OFDM symbols per slot * <NUM> slots per second) = <NUM> Mbps. This roughly corresponds to the capacity of an illustrative bottleneck fronthaul link. The bandwidth of <NUM>, which means <NUM> RBs, and <NUM> number of user layers chosen is used here only for sake of simplicity. However, the results can be scaled arbitrarily. With the dimensioning rule of thumb described above, or any other not covering the absolute peak fronthaul demand, it is possible that fluctuations in demand could temporarily overload this network, causing unwanted congestion. Consider the case that in the first three slots, which are downlink slots, A<NUM> is always at peak usage (DDD) and A<NUM> and A<NUM> are at <NUM>/<NUM> peak (DDX), where "X" means a slot without assignments or grants. However, in a particularly busy slot, A<NUM> happens to have extra demand. Then the following situation occurs:.

The total demand is as shown in Table <NUM>, <NUM> Mbps in the particularly busy slot, but as the fronthaul capacity is <NUM> Mbps, a congestion state may occur. Since a congestion state can be difficult to recover from, it is useful to limit the cell's peak usage to respect the fronthaul limitations. Because there are no cell-specific restrictions so far, the fronthaul controller according to embodiments calculates such restrictions. The restrictions may be applied as equal-share allocation and realized in several ways, out of which four possible options are shown in Table <NUM> below:.

An equal share allocation could be that the time unit transmission restrictions for the first base stations system <NUM> and the time unit transmission restrictions for the second base station system <NUM> are mutually distributed so that available transmission resources for the first base station system and available transmission resources for the second base station system are proportional to the required capacity for transmission and/or reception of wireless signals by the first base station system <NUM> and the required capacity for transmission and/or reception of wireless signals by the second base station system <NUM>. Note that in some cases, e.g. options (<NUM>)-(<NUM>) above, a longer sequence of slot formats was necessary to respect the harmonized transmission scheme. For simplicity, suppose option (<NUM>) above was chosen. In the Xn interface, the cells can communicate with each other, via e.g. Load Management messages, their current and/or predicted load for the near future. In this example, suppose cell A<NUM> informs a predicted increase in usage, while the fronthaul controller can observe that cell A<NUM>'s load has been consistently below average.

With this input, the fronthaul controller can reallocate some of A<NUM>'s resources to A<NUM>, as shown in Table <NUM> below. It is straightforward to obtain a non-equal allocation with this scheme as well.

By the methods, systems and BBUs described in this disclosure, a way is provided for the wireless communication network including the base station systems to respect fronthaul network limitations without introducing awareness of the state of the fronthaul network in the scheduler: the latter is merely constrained by how many assignments, or grants, it can distribute. This is achieved while respecting the harmonized transmission scheme over the air. Note that while the examples describe full slot limitations it is also possible to get finer granularity by restricting usage on an OFDM symbol basis.

<FIG>, in conjunction with <FIG>, shows a system <NUM> configured for a wireless communication network comprising a plurality of base station systems <NUM>, <NUM>. Each base station system comprises a BBU <NUM>, <NUM> and an RU <NUM>, <NUM> interconnected via a fronthaul connection <NUM>. The RUs <NUM>, <NUM> are arranged to transmit wireless signals to, and receive from, wireless communication devices <NUM>, <NUM>. The system <NUM> comprises a processing circuitry <NUM> and a memory <NUM>. Said memory contains instructions executable by said processing circuitry, whereby the system <NUM> is operative for obtaining fronthaul capacity information on transmission capacity of a part of the fronthaul connection <NUM> that is shared by a first base station system <NUM> and a second base station system <NUM> of the plurality of base station systems, and obtaining information on required capacity for transmission and/or reception of wireless signals by the RU <NUM> of the first base station system <NUM> and by the RU <NUM> of the second base station system <NUM> towards and/or from the wireless communication devices <NUM>, <NUM>. The system is further operative for determining time unit transmission restrictions for the first base station system <NUM> and for the second base station system <NUM> based on the obtained fronthaul capacity information and on the obtained information on required capacity, which time unit transmission restrictions results in fronthaul usage below the transmission capacity of the part of the fronthaul connection, and sending information on the determined time unit transmission restrictions for the first base station system to the BBU of the first base station system and information on the determined time unit transmission restrictions for the second base station system to the BBU of the second base station system.

The system <NUM> may be called a fronthaul controller. The fronthaul controller could be situated anywhere inside or outside the wireless communication network. According to one embodiment, the fronthaul controller is situated close to any of the BBUs, or even in one of the BBUs in order to be able to perform fast instructions. Alternatively, the fronthaul controller may be realized as a group of network nodes, wherein functionality of the fronthaul controller is spread out over different physical, or virtual, nodes, a so called cloud-solution.

According to an embodiment, the determined time unit transmission restrictions comprises a first mask defining at which time units no data is to be sent between the BBU <NUM> of the first base station system <NUM> and its RU <NUM> and a second mask defining at which time units no data is to be sent between the BBU <NUM> of the second base station system <NUM> and its RU <NUM>. Further, the information that the system is operable for sending to the BBU <NUM> of the first base station system <NUM> is the first mask and the information that the system is operable for sending to the BBU <NUM> of the second base station system <NUM> is the second mask.

According to another embodiment, the system is further operative for, for time units that are configured as uplink time units: initiating sending of the determined time unit transmission restrictions for the first base station system to the RU <NUM> of the first base station system <NUM>, and initiating sending of the determined time unit transmission restrictions for the second base station system to the RU <NUM> of the second base station system <NUM>.

According to another embodiment, the time unit transmission restrictions define for which time units no grants are to be distributed by the BBU <NUM> of the first base station system <NUM> towards its RU <NUM> and for which time units no grants are to be distributed by the BBU <NUM> of the second base station system <NUM> towards its RU <NUM>.

According to another embodiment, the time unit transmission restrictions for the first base stations system <NUM> and the time unit transmission restrictions for the second base station system <NUM> are mutually distributed so that available transmission resources for the first base station system and available transmission resources for the second base station system are proportional to the required capacity for transmission and/or reception of wireless signals by the first base station system <NUM> and the required capacity for transmission and/or reception of wireless signals by the second base station system <NUM>.

According to another embodiment, the system is further operative for obtaining information on utilization of transmission resources of the first base station system and information on utilization of transmission resources of the second base station system when the determined time unit restrictions of the first and the second base station system are used, and for adapting the determined time unit transmission restrictions of the first base station system and the time unit transmission restrictions of the second base station system to the obtained information on utilization of transmission resources of the first base station system and information on utilization of transmission resources of the second base station system. Further, the system is operative for sending information on the respective adapted time unit transmission restriction to the respective one of the first and the second base station system.

According to other embodiments, the system <NUM> may further comprise a communication unit <NUM>, which may be considered to comprise conventional means for communication with the BBUs of the first and second base station system as well as with other base stations or base station systems. The instructions executable by said processing circuitry <NUM> may be arranged as a computer program <NUM> stored e.g. in said memory <NUM>. The processing circuitry <NUM> and the memory <NUM> may be arranged in a sub-arrangement <NUM>. The sub-arrangement <NUM> may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s)/processing circuit(s) configured to perform the methods mentioned above. The processing circuitry <NUM> may comprise one or more programmable processor, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.

The computer program <NUM> may be arranged such that when its instructions are run in the processing circuitry, they cause the system <NUM> to perform the steps described in any of the described embodiments of the system <NUM> and its method. The computer program <NUM> may be carried by a computer program product connectable to the processing circuitry <NUM>. The computer program product may be the memory <NUM>, or at least arranged in the memory. The memory <NUM> may be realized as for example a RAM (Random-access memory), ROM (Read-Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). Further, the computer program <NUM> may be carried by a separate computer-readable medium, such as a CD, DVD or flash memory, from which the program could be downloaded into the memory <NUM>. Alternatively, the computer program may be stored on a server or any other entity to which the system <NUM> has access via the communication unit <NUM>. The computer program <NUM> may then be downloaded from the server into the memory <NUM>.

<FIG>, in conjunction with <FIG>, shows a BBU <NUM> operable in a first base station system <NUM> of a wireless communication network, the first base station system <NUM> further comprising an RU <NUM>. Further, the wireless communication network comprises a second base station system comprising an RU and a BBU. The BBUs and the RUs of each base station system are interconnected via a fronthaul connection <NUM>. The fronthaul connection is shared by the first and the second base station system. The BBU <NUM> comprises a processing circuitry <NUM> and a memory <NUM>. Said memory contains instructions executable by said processing circuitry, whereby the BBU <NUM> is operative for receiving, from a system <NUM> related to the wireless communication network, information on time unit transmission restrictions for the first base station system <NUM>, the time unit transmission restrictions being determined based on fronthaul capacity information on the shared fronthaul connection and on information on required capacity for transmission and/or reception of wireless signals by the RU <NUM> of the first base station system <NUM> and by the RU of the second base station system <NUM>. The BBU is further operative for allocating transmission resources according to the information on time unit transmission restrictions. and for triggering communication of signals over the allocated transmission resources with wireless communication devices <NUM> connected to the RU of the first base station system <NUM>, according to the allocation.

According to an embodiment, the received information on time unit transmission restrictions defines for which time units no grants are to be distributed by the BBU <NUM> of the first base station system <NUM> towards its RU <NUM>.

According to another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a certain time unit, the BBU is operative for reconfiguring downlink transmission resources in that certain time unit into uplink transmission resources, and for triggering sending of information on the reconfiguration towards wireless communication devices <NUM> connected to the RU <NUM> of the first base station system <NUM>.

According to another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a particular time unit, which time unit is set as downlink, the BBU is operative for reconfiguring a DRX cycle for wireless communication devices <NUM> connected to the RU <NUM> so that the wireless communication devices <NUM> are informed that no signals are to be received at that particular time unit, and for triggering sending of information on the reconfiguring to the wireless communication devices <NUM>.

According to another embodiment, when the information on time unit transmission restrictions reveals that no signals are to be sent in a given time unit, which time unit is set as downlink, the BBU is operative for sending information on the time unit transmission restrictions of the given time unit to another base station system that is not using the shared fronthaul connection.

According to other embodiments, the BBU <NUM> may further comprise a communication unit <NUM>, which may be considered to comprise conventional means for communication with the system <NUM> as well as with the RU <NUM>. The instructions executable by said processing circuitry <NUM> may be arranged as a computer program <NUM> stored e.g. in said memory <NUM>. The processing circuitry <NUM> and the memory <NUM> may be arranged in a sub-arrangement <NUM>. The sub-arrangement <NUM> may be a micro-processor and adequate software and storage therefore, a Programmable Logic Device, PLD, or other electronic component(s)/processing circuit(s) configured to perform the methods mentioned above. The processing circuitry <NUM> may comprise one or more programmable processor, application-specific integrated circuits, field programmable gate arrays or combinations of these adapted to execute instructions.

The computer program <NUM> may be arranged such that when its instructions are run in the processing circuitry, they cause the BBU <NUM> to perform the steps described in any of the described embodiments of the BBU <NUM> and its method. The computer program <NUM> may be carried by a computer program product connectable to the processing circuitry <NUM>. The computer program product may be the memory <NUM>, or at least arranged in the memory. The memory <NUM> may be realized as for example a RAM (Random-access memory), ROM (Read-Only Memory) or an EEPROM (Electrical Erasable Programmable ROM). Further, the computer program <NUM> may be carried by a separate computer-readable medium, such as a CD, DVD or flash memory, from which the program could be downloaded into the memory <NUM>. Alternatively, the computer program may be stored on a server or any other entity to which the BBU <NUM> has access via the communication unit <NUM>. The computer program <NUM> may then be downloaded from the server into the memory <NUM>.

Claim 1:
A method performed by a system (<NUM>) related to a wireless communication network comprising a plurality of base station systems (<NUM>, <NUM>), each base station system comprising a baseband unit, BBU (<NUM>, <NUM>) and a radio unit, RU (<NUM>, <NUM>) interconnected via a fronthaul connection (<NUM>), the RUs (<NUM>, <NUM>) being arranged to transmit wireless signals to, and receive from, wireless communication devices (<NUM>, <NUM>), the method comprising:
obtaining (<NUM>) fronthaul capacity information on transmission capacity of a part of the fronthaul connection (<NUM>) that is shared by a first base station system (<NUM>) and a second base station system (<NUM>) of the plurality of base station systems;
obtaining (<NUM>) information on required capacity for transmission and/or reception of wireless signals by the RU (<NUM>) of the first base station system (<NUM>) and by the RU (<NUM>) of the second base station system (<NUM>) towards and/or from the wireless communication devices (<NUM>, <NUM>);
determining (<NUM>) time unit transmission restrictions for the first base station system (<NUM>) and for the second base station system (<NUM>) based on the obtained (<NUM>) fronthaul capacity information and on the obtained (<NUM>) information on required capacity, which time unit transmission restrictions results in fronthaul usage below the transmission capacity of the part of the fronthaul connection, and
sending (<NUM>) information on the determined time unit transmission restrictions for the first base station system to the BBU of the first base station system and information on the determined time unit transmission restrictions for the second base station system to the BBU of the second base station system.