Frequency location of a PCell

There is provided mechanisms for determining frequency location of a primary cell (PCell) for a wireless device in a carrier aggregation supported communications network having access to a group of low frequency bands and a group of high frequency bands. A method is performed by a network node. The method comprises acquiring an uplink load level for the group of low frequency bands. The method comprises acquiring a pathloss level between a wireless device served by the communications network and the network node. The method comprises selecting, from the acquired uplink load level and pathloss level, which one of the group of low frequency bands and the group of high frequency bands to place the frequency location of the PCell for the wireless device.

PRIORITY

This nonprovisional application is a U.S. National Stage Filing under 35 U.S.C. § 371 of International Patent Application Serial No. PCT/SE2015/050945 filed Sep. 8, 2015, and entitled “FREQUENCY LOCATION OF A PCELL.”

TECHNICAL FIELD

Embodiments presented herein relate to a method, a network node200, a computer program, and a computer program product for determining frequency location of a primary serving cell (PCell).

BACKGROUND

In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

For example, to cope with increasing mobile traffic capacity demands and higher expectations for better user experience, operators have started to deploy multiple frequency carriers in radio access network nodes. In wireless technologies, such as the long term evolution (LTE) telecommunications standards, multiple frequency carriers can be assigned from both low frequency bands (e.g. 700-900 MHz) and high frequency bands (e.g. 1800-3500 MHz). For next generation wireless technologies even higher frequency bands are being considered (e.g. up to 100 GHz). The bandwidth is usually limited in the low frequency bands compared to the high frequency bands. Common allocations include e.g. 10 MHz in the low frequency bands and e.g. 20 MHz in the high frequency bands for an operator. It is also common that an operator has allocations from both low frequency bands and high frequency bands. The low frequency bands are well suited for high range coverage and indoor coverage due to better propagation characteristics than the high frequency bands, whilst the high frequency bands have shorter range coverage but can provide higher capacity than the low frequency bands due to the larger bandwidth. Carrier aggregation (CA) can be used in the downlink (i.e., transmission from radio access network node to wireless device) to aggregate carriers in order to increase bandwidth when scheduling data for a wireless device. Carrier aggregation can also be used in uplink. Mobile broadband services are downlink heavy since multimedia services, such as streaming video services, are growing in popularity. Downlink services based on the Transmission Control Protocol (TCP) requires feedback from the wireless device; otherwise there can be no downlink throughput and service will degrade.

The LTE Rel-10 specifications have been standardized. The LTE Rel-10 specifications provide support for so-called Component Carrier (CC) bandwidths up to 20 MHz (which is the maximum LTE Rel-8 carrier bandwidth). An LTE Rel-10 operation wider than 20 MHz is possible and appear as a number of LTE CCs to an LTE Rel-10 supporting wireless device. One way to obtain bandwidths wider than 20 MHz is by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10 supporting wireless device is able to receive multiple CCs, where the CCs have, or at least the possibility to have, the same structure as a Rel-8 carrier. CA is illustrated inFIG. 6.FIG. 6schematically illustrates an aggregated bandwidth610along which component carriers620a,620b, . . . ,620nare placed. The aggregated bandwidth610may for example be 100 MHz and each component carrier620a,620b, . . . ,620nmay occupy a bandwidth 20 MHz.

The Rel-10 specifications provide support for up to five aggregated CCs where each CC is limited in the radio frequency (RF) specifications to have one of six available bandwidths, namely 6, 15, 25, 50, 75 or 100 resource blocks (RB), corresponding to bandwidths of 1.4, 3 5 10 15 and 20 MHz, respectively.

The number of aggregated CCs as well as the bandwidth of the individual CCs may be different for uplink (i.e., transmission from wireless device to radio access network node) and downlink. A symmetric configuration refers to the case where the number of CCs in downlink (DL) and uplink (UL) is the same whereas an asymmetric configuration refers to the case that the number of CCs is different in DL and UL. The number of CCs configured in the communications network may be different from the number of CCs seen by a wireless device; a wireless device may, for example, support more downlink CCs than uplink CCs, even though the communications network offers the same number of uplink and downlink CCs.

CCs are also referred to as cells or serving cells. More specifically, in an LTE network the cells aggregated by a wireless device are denoted primary Serving Cell (PCell) and secondary Serving Cells (SCells). The term serving cell is defined to encompass both PCell and SCells. All wireless devices have one PCell. Which cell is the PCell for a wireless device is wireless device specific. The PCell is, from a signalling perspective, considered more important than the SCells; vital control signaling and other important signaling is typically handled via the PCell. Uplink control signaling is currently always sent on the PCell. The component carrier configured as the PCell is the Primary CC (PCC) whereas all other component carriers configured as the SCells are Secondary (SCC). The wireless device can send and receive data both on the PCell and SCells. Some control signaling, such as scheduling commands, could either be configured to only be transmitted and received on the PCell but where the commands are also valid for the SCell, or can be configured to be transmitted and received on both the PCell and the SCells. Regardless of the mode of operation, the wireless device will only need to read the broadcast channel in order to acquire system information parameters on the PCC. System information related to SCC may be provided to the wireless device in dedicated Radio Resource Control (RRC) messages.

During initial access an LTE Rel-10 supporting wireless device behaves similar to a LTE Rel-8 supporting wireless device. However, upon successful connection to the network a Rel-10 supporting wireless device may—depending on its own capabilities and the capabilities of the network—be configured with additional serving cells in the UL and/or DL. Configuration is based on RRC. Due to the heavy signaling and rather slow speed of the RRC signaling it is envisioned that a wireless device may be configured with multiple serving cells, even though not all of them are currently used.

Different deployment scenarios for carrier aggregation in relation to frequency bands and the placement of cells within frequency bands are shown at (a), (b), and (c) inFIG. 7.FIG. 7schematically illustrates a group of low frequency bands710a,710b,710c, a group of high frequency bands720a,720b,720c, and a group of mid frequency bands730a,730b,730c. The groups of low frequency bands710b,710cfurther comprises a further group of low frequency bands710ba,710caand a further group of high frequency bands710bb,710cb. There are different ways to place cells (PCell or SCell)740a,740b,740cin the frequency bands. The different variants are intra-band aggregation, contiguous cells as in (b), intra-band aggregation, non-contiguous cells as in (c), and inter-band aggregation as in (a).

To summarize, LTE CA supports efficient use of multiple carriers, allowing data to be sent and/or received over all carriers. There is support for cross-carrier scheduling avoiding the need for the wireless device to listen to all carrier-scheduling channels all the time. This mechanism relies on tight time synchronization between the carriers.

An issue with deploying multiple frequency carriers to radio access network nodes is that different frequency bands have different performance characteristics. This is especially seen for wireless devices located at large distances from the serving radio access network node or at indoor locations with high pathloss to the serving radio access network node.FIG. 8shows the uplink cell edge throughput (5:th percentage) for simulations of a low frequency band (900 MHz) and a high frequency band (2600 MHz). It can be seen that the high frequency band offers no throughput at the cell edge in this scenario. The low frequency band offers better throughput but may on the other hand suffer from increased interference as the load increases (as represented by the increased curve slope) due to better propagation characteristics in this frequency band.

There is hence a need for providing a reliable uplink in deployments with more than one available frequency band.

SUMMARY

A particular object of embodiments herein is therefore to provide a reliable uplink in deployments with more than one available frequency band.

The inventors of the herein disclosed embodiments have realized that, with carrier aggregation, selecting what frequency band to use as PCell is important as it carries uplink signaling. Selecting e.g., the PCell to be located at 2600 MHz as in the scenario fromFIG. 8can result in unsatisfactory downlink performance since the uplink performance at the high frequency band is very poor. Commonly, the PCell is placed in the low frequency band. However, the inventors of the herein disclosed embodiments have further realized that an issue with always selecting the low frequency band for the PCell is that the low frequency band can become overloaded and suffer from high interference with degraded performance as a result.

A particular object of embodiments herein is therefore to provide efficient determination of frequency location of the PCell for a wireless device.

According to a first aspect there is presented a method for determining frequency location of a primary cell (PCell) for a wireless device in a carrier aggregation supported communications network having access to a group of low frequency bands and a group of high frequency bands. The method is performed by a network node. The method comprises acquiring an uplink load level for the group of low frequency bands. The method comprises acquiring a pathloss level between a wireless device served by the communications network and the network node. The method comprises selecting, from the acquired uplink load level and pathloss level, which one of the group of low frequency bands and the group of high frequency bands to place the frequency location of the PCell for the wireless device.

Advantageously this provides reliable uplink in deployments with more than one available frequency band.

Advantageously this provides efficient determination of frequency location of the PCell for the wireless device.

Advantageously this enables improved uplink reliability, throughput and capacity compared to traditional mechanisms.

Advantageously this enables better carrier aggregation and downlink performance than traditional mechanisms since the PCell is selected such that uplink signaling (using the PCell) can be secured.

According to a second aspect there is presented a network node for determining frequency location of a PCell for a wireless device in a carrier aggregation supported communications network having access to a group of low frequency bands and a group of high frequency bands. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to perform a set of operations. The processing circuitry is configured to cause the network node to acquire an uplink load level for the group of low frequency bands. The processing circuitry is configured to cause the network node to acquire a pathloss level between a wireless device served by the communications network and the network node. The processing circuitry is configured to cause the network node to select, from the acquired uplink load level and pathloss level, which one of the group of low frequency bands and the group of high frequency bands to place the frequency location of the PCell for the wireless device.

According to a third aspect there is presented a network node for determining frequency location of a PCell for a wireless device in a carrier aggregation supported communications network having access to a group of low frequency bands and a group of high frequency bands. The network node comprises processing circuitry. The network node comprises a computer program product. The computer program product stores instructions that, when executed by the processing circuitry, causes the network node to perform a method according to the first aspect.

According to a fourth aspect there is presented a computer program for determining frequency location of a PCell for a wireless device, the computer program comprising computer program code which, when run on a network node, causes the network node to perform a method according to the first aspect.

According to a fifth aspect there is presented a computer program product comprising a computer program according to the fourth aspect and a computer readable medium on which the computer program is stored.

It is to be noted that any feature of the first, second, third, fourth and fifth aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, and/or fifth aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

DETAILED DESCRIPTION

FIG. 1is a schematic diagram illustrating a communications network100where embodiments presented herein can be applied. The communications network100comprises radio access network nodes120configured to provide network coverage to wireless devices110a,110bin a cell130. As understood by the skilled person the communications network100may comprise a plurality of such radio access network nodes120, each providing network coverage to wireless devices110a,110bin its own cell. The radio access network nodes120may be provided as any combination of radio base stations, base transceiver stations, node Bs, evolved node Bs, or other wireless access points. The wireless devices110a,110bmay be provided as any combination of mobile stations, mobile phones, handsets, wireless local loop phones, user equipment (UE), smartphones, laptop computers, tablet computers, wireless modems, and network equipped sensors.

The radio access network nodes120are operatively connected to a core network140which in turn is operatively connected to s service network150. The wireless devices110a,110bare thereby enabled to access services and exchange data with the service network150. The communications network100further comprises at least one network node200.FIG. 1schematically illustrates different locations of the network node200. For example, a network node200may be located in a radio access network node120, as a separate entity in a radio access network as defined by the radio access network nodes120, as an entity in the core network140and/or as an entity in the service network150. Further description of the network node200will be provided below.

The communications network100is assumed to support carrier aggregation having access to at least a group of low frequency bands710a,710b,710cand a group of high frequency bands720a,720b,720c, seeFIG. 7as described above. In a radio access network node120supporting carrier aggregation using multiple frequency bands (such as a group of low frequency bands710a,710b,710cand a group of high frequency bands720a,720b,720c), there may be different ways to select the frequency location of the PCell (740a,740b, or740c). In general terms, carrier aggregation can be regarded as a special case of dual connectivity where, for example, one network node200is configured to support communications on a first group of frequency bands when communicating with a wireless device110a,110band where another network node200is configured to support communications on a second group of frequency bands when communicating with the same wireless device110a,110b. Hence, the terms carrier aggregation and dual connectivity may be used interchangeably throughout this disclosure.

The embodiments disclosed herein relate to such determination of the frequency location of a PCell for the wireless device110a,110b. In order to obtain such determination there is provided a network node200, a method performed by the network node200, a computer program comprising code, for example in the form of a computer program product, that when run on a network node200, causes the network node200to perform the method.

FIG. 2aschematically illustrates, in terms of a number of functional units, the components of a network node200according to an embodiment. Processing circuitry210is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product310(as inFIG. 3), e.g. in the form of a storage medium230.

Particularly, the processing circuitry210is configured to cause the network node200to perform a set of operations, or steps, S102-S112. These operations, or steps, S102-S112will be disclosed below. For example, the storage medium230may store the set of operations, and the processing circuitry210may be configured to retrieve the set of operations from the storage medium230to cause the network node200to perform the set of operations. The set of operations may be provided as a set of executable instructions.

Thus the processing circuitry210is thereby arranged to execute methods as herein disclosed. The storage medium230may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The network node200may further comprise a communications interface220for communications with at least one wireless device110a,110b, another network node200as well as nodes, devices, and entities in the core network140or the service network150. As such the communications interface220may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for wireless communications and ports for wireline communications. The processing circuitry210controls the general operation of the network node200e.g. by sending data and control signals to the communications interface220and the storage medium230, by receiving data and reports from the communications interface220, and by retrieving data and instructions from the storage medium230. Other components, as well as the related functionality, of the network node200are omitted in order not to obscure the concepts presented herein.

FIG. 2bschematically illustrates, in terms of a number of functional modules210a-210d, the components of a network node200according to an embodiment. The functionality of each functional module210a-210dwill be further disclosed below in the context of which the functional modules210a-210dmay be used. The network node200ofFIG. 2bcomprises an acquire module210aconfigured to perform below steps S102, S104, S106, and a select module210bconfigured to perform below step S108. The network node200ofFIG. 2bmay further comprises a number of optional functional modules, such as any of a divide module210C configured to perform below step S110, and/or a determine module210dconfigured to perform below step S112. In general terms, each functional module210a-210dmay in one embodiment be implemented only in hardware or and in another embodiment with the help of software, i.e., the latter embodiment having computer program instructions stored on the storage medium230which when run on the processing circuitry makes the network node200perform the corresponding steps mentioned above in conjunction withFIG. 2b. It should also be mentioned that even though the modules correspond to parts of a computer program, they do not need to be separate modules therein, but the way in which they are implemented in software is dependent on the programming language used. Preferably, one or more or all functional modules210a-210dmay be implemented by the processing circuitry210, possibly in cooperation with functional units220and/or230. The processing circuitry210may thus be configured to from the storage medium230fetch instructions as provided by a functional module210a-210dand to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

The network node200may be provided as a standalone device or as a part of at least one further device. For example, the network node200may be provided in a node of the radio access network (such as in a radio access network node120) or in a node of the core network140or in a node of the service network150. Alternatively, functionality of the network node200may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network or the core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell130than instructions that are not required to be performed in real time. In this respect, at least part of the network node200may reside in the radio access network, such as in the radio access network node120, for cases when embodiments as disclosed herein are performed in real time.

Thus, a first portion of the instructions performed by the network node200may be executed in a first device, and a second portion of the of the instructions performed by the network node200may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node200may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node200residing in a cloud computational environment. Therefore, although a single processing circuitry210is illustrated inFIG. 2athe processing circuitry210may be distributed among a plurality of devices, or nodes. The same applies to the functional modules210a-210dofFIG. 2band the computer program320ofFIG. 3(see below).

FIG. 3shows one example of a computer program product310comprising computer readable medium330. On this computer readable medium330, a computer program320can be stored, which computer program320can cause the processing circuitry210and thereto operatively coupled entities and devices, such as the communications interface220and the storage medium230, to execute methods according to embodiments described herein. The computer program320and/or computer program product310may thus provide means for performing any steps as herein disclosed.

FIGS. 4 and 5are flow chart illustrating embodiments of methods for determining frequency location of a PCell. The methods are performed by the network node200. The methods are advantageously provided as computer programs320.

Reference is now made toFIG. 4illustrating a method for determining frequency location of a PCell for the wireless device110a,110bas performed by the network node200according to an embodiment. Continued references are made toFIGS. 1, 2a,2b, and7.

The frequency location of the PCell for the wireless device110a,110bis determined in a carrier aggregation supported communications network100where access is enabled to at least a group of low frequency bands710a,710b,710cand a group of high frequency bands720a,720b,720c.

The frequency location of the PCell is at least based on uplink load level and pathloss level. The network node200is therefore configured to, in a step S104, acquire an uplink load level for the group of low frequency bands710a,710b,710c. In this respect the acquire module210amay comprise instructions that when executed by the network node200causes the processing circuitry210, possible in conjunction with the communications interface220and the storage medium230, to acquire the uplink load level in order for the network node200to perform step S104. Examples of how the uplink load level may be measured will be provided below.

Further, the network node200is configured to, in a step S106, acquire a pathloss level between the wireless device110a,110bserved by the communications network100and the network node200. In this respect the acquire module210amay comprise instructions that when executed by the network node200causes the processing circuitry210, possible in conjunction with the communications interface220and the storage medium230, to acquire the pathloss in order for the network node200to perform step S106. Examples of how the pathloss level may be measured will be provided below.

The network node200is then configured to, in a step S108, select, from the acquired uplink load level and pathloss level, which one of the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720cto place the frequency location of the PCell for the wireless device110a,110bin. In this respect the select module210bmay comprise instructions that when executed by the network node200causes the processing circuitry210to select the group in order for the network node200to perform step S108. Examples of how the group in which the frequency location of the PCell is placed will be provided below.

Embodiments relating to further details of determining frequency location of a PCell for the wireless device110a,110bwill now be disclosed.

There may be different examples of uplink load level. For example, the uplink load level may represent an uplink interference level, an uplink resource utilization level, an uplink traffic throughput level, or any combination thereof.

There may be different examples of how the uplink load level may be measured. For example, a measure of the uplink load level can be how many of the available uplink radio resources that are occupied. That is, the uplink load level may represent the number of available uplink radio resources in the group of low frequency bands710a,710b,710cthat are occupied. Further, the uplink load level may be determined based on uplink throughput statistics in the communications network100.

The uplink load level may be measured for an uplink control channel and/or uplink data channel, such as an uplink data channel used for transmission of acknowledgement messages. One example of acknowledgement messages is TCP acknowledgement messages; both ACKs and NACKs. That is, the uplink load level may be for an uplink control channel, an uplink data channel used for transmission of acknowledgement messages, or any combination thereof.

There may be different examples of pathloss levels to be considered. For example, the pathloss can be estimated by the network node200in the uplink or from downlink measurements reports received from the wireless device110a,110b. That is, the pathloss level may be derived from uplink measurements, downlink measurements reports received from the wireless device110a,110b, or any combination thereof. Further, the pathloss may be estimated during a handover evaluation process. That is, the downlink measurements report may be part of a handover evaluation process of the wireless device110a,110bor measurements may be triggered separately.

The pathloss level may be determined for the group of low frequency bands710a,710b,710c, from the group of high frequency bands720a,720b,720c, or any combination thereof.

There may be different ways to determine which frequency bands to include in the group of low frequency bands710a,710b,710cand which frequency bands to include in the group of high frequency bands720a,720b,720c. According to an embodiment, frequency bands located lower than 1 GHz belong to the group of low frequency bands710a,710b,710cand frequency bands located at 1 GHz or higher belong to the group of high frequency bands720a,720b,720c. However, as the skilled person understands, this frequency threshold between the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720cmay be set differently, for example depending on which frequency bands that are available. According to another embodiment the threshold frequency to separate the group of low frequency bands710a,710b,710cfrom the group of high frequency bands720a,720b,720cis set higher, such as between 1 GHz and 1700 MHz or even higher, such as between 1700 MHz and 2600 MHz.

For example, the carrier aggregation supported communications network100may further comprise a group of mid frequency bands730a,730b,730cand hence there may be two frequency thresholds in order to separate the group of mid frequency bands730a,730b,730cfrom the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720c. In some embodiment each frequency band in the group of mid frequency bands730a,730b,730cis merged with one of the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720c, respectively. In other embodiments this group of mid frequency bands730a,730b,730cis discarded when selecting the frequency location for the PCell. Further, as will be further disclosed below, a group of frequency bands may in turn be split into two (sub-)groups of frequency bands.

There may be different ways for the network node200to select, from the acquired uplink load level and pathloss level, which one of the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720cto place the frequency location of the PCell for the wireless device110a,110bin, as in step S108. Different embodiments relating thereto will now be described in turn.

According to one embodiment, as long as the uplink load level of the group of low frequency bands710a,710b,710cis below a first predetermined level, the group of low frequency bands710a,710b,710cis used as PCell in the communication with the wireless device110a,110b. That is, the frequency location of the PCell may be selected to be in the group of low frequency bands710a,710b,710cif the uplink load level for the group of low frequency bands710a,710b,710cis below a first predetermined level.

According to one embodiment, when the uplink load level of the group of low frequency bands710a,710b,710cexceeds the first predetermined level, also the pathloss between the wireless device110a,110band radio access network node120is considered in the PCell selection. That is, the frequency location of the PCell may be selected based only on the pathloss level but no longer on the uplink load level if the uplink load level for the group of low frequency bands710a,710b,710cis above the first predetermined level. That is, the uplink load level no longer considered in the selection of the frequency location of the PCell when it has been established that the uplink load level is above the first predetermined level.

According to one embodiment, if the pathloss is below a second predetermined limit, the group of high frequency bands720a,720b,720cis selected as PCell. That is, the frequency location of the PCell may be selected to be in the group of high frequency bands720a,720b,720cif the pathloss level is below the second predetermined level.

According to one embodiment, the group of low frequency bands710a,710b,710cis selected as PCell if the pathloss is above the second predetermined limit. That is, the frequency location of the PCell may be selected to be in the group of low frequency bands710a,710b,710cif the pathloss level is above the second predetermined level.

According to one embodiment, the PCell is randomly selected between the the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720cif the pathloss is below the second predetermined limit. That is, the frequency location of the PCell may be randomly selected between the group of high frequency bands720a,720b,720cand the group of low frequency bands710a,710b,710cif the pathloss level is below a second predetermined level.

There may be different ways to determine the first predetermined level and the second predetermined level, respectively. Different embodiments relating thereto will now be described in turn.

According to one embodiment the first predetermined level is selected, or tuned, based on uplink performance statistics; medium or average throughput or any other percentile of throughput, over many load situations, depending on the desired target (e.g. cell edge or median throughput). That is, the first predetermined level may be based on uplink performance statistics in the communications network100.

According to one embodiment the second predetermined limit is determined, or tuned, in a similar way as the first predetermined limit by observing and analyzing uplink performance statistics whilst varying the second predetermined limit. This determination, or tuning, is not load dependent. That is, the second predetermined level may be based on uplink performance statistics in the communications network100.

Reference is now made toFIG. 5illustrating methods for determining frequency location of the PCell for the wireless device110a,110bas performed by the network node200according to further embodiments. Continued references are made toFIGS. 1, 2a,2b, and7.

There may be different ways for the network node200to determine when to determine the frequency location of the PCell for the wireless device110a,110b. For example, the network node200may be configured to, in a step S102, acquire a need for carrier aggregation for the wireless device110a,110b. In this respect the acquire module210amay comprise instructions that when executed by the network node200causes the processing circuitry210, possible in conjunction with the communications interface220and the storage medium230, to acquire the need for carrier aggregation in order for the network node200to perform step S102. The uplink load level may then be acquired in response thereto.

There are different examples of needs that the network node200can acquire in step S102. For example, the need may represent an indication that the amount of buffered data in the network node200is higher than a third predetermined level, an indication that the wireless device110a,110bis in active mode, an indication that the wireless device110a,110bsupports carrier aggregation, that uplink performance is below a fourth predetermined level, or any combination thereof. The third predetermined level and the fourth predetermined level may be determined so as to tune the performance of the determination of the frequency location of the PCell for the wireless device110a,110baccording to network demands as well as operator demands; too frequent performance of the determination of the frequency location of the PCell for the wireless device110a,110bmay result in an unstable communications network100, whilst too seldom performance may result in available network resources, such as carrier aggregation, are not utilized.

Further, the determination of the frequency location of the PCell for the wireless device110a,110bmay be performed either during CA (carrier aggregation) use or before CA is to be used (as part of setting up CA). That is, the step of selecting which of the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720cto place the frequency location of the PCell may be performed during ongoing carrier aggregation of the wireless device110a,110b, or as part of setting up carrier aggregation for the wireless device110a,110b.

The determination of the frequency location of the PCell for the wireless device110a,110bmay be performed in an iterative manner. That is, according to one embodiment the group of frequency bands in which the frequency location of the PCell is placed is iteratively selected.

One example of such an iterative procedure for selecting the frequency location of the PCell for the wireless device110a,110bwill now be described. However, as the skilled person understands, there may be other iterative procedures for selecting the frequency location of the PCell for the wireless device110a,110b. In brief, the selected group of frequency bands (as selected in step S108) may in turn divided into a new group of low frequency bands and new group of high frequency bands.

In more detail, the network node200may be configured to, in a step S110, divide the selected group of frequency bands in which the frequency location of the PCell has been placed into a further group of low frequency bands (710baor710ca) and a further group of high frequency bands (710bb, or710cb). In this respect the divide module210cmay comprise instructions that when executed by the network node200causes the processing circuitry210to divide these selected group of frequency bands in order for the network node200to perform step S110. The network node200may then be configured to, in a step S112, determine, from the acquired uplink load level and pathloss level, the frequency location of the PCell to be in either the further group of low frequency bands (710ba, or710ca) or the further group of high frequency bands (710bb, or710cb). In this respect the determine module210dmay comprise instructions that when executed by the network node200causes the processing circuitry210to determine, from the acquired uplink load level and pathloss level, the frequency location of the PCell in order for the network node200to perform step S112.

FIG. 9shows simulation results of uplink performance with the group of low frequency bands710a,710b,710cand the group of high frequency bands720a,720b,720ccombined in the same scenario as inFIG. 8. Performances of two of the herein disclosed embodiments are illustrated at910and920, respectively. The plot at910represents the above disclosed embodiment of randomly select the group of frequency bands when the pathloss is low (i.e., below the second predetermined limit). The plot at920represents the above disclosed embodiment of selecting the group of high frequency bands720a,720b,720cwhen the pathloss is low and the group of low frequency bands710a,710b,710cwhen the pathloss is high (i.e., above the second predetermined limit). Commonly for these two embodiments is that a frequency in the group of low frequency bands710a,710b,710cis always selected as PCell at low uplink loads, but as the uplink load increases the group of high frequency bands720a,720b,720cis used for selected wireless devices110a,110bdepending on their pathloss. The result is increased capacity and throughput at higher loads. For example, the maximum traffic is increased from 0.08 to 0.12 or 0.16, i.e. 50-100% higher.

Further, the solid lines marked by squares and diamonds inFIG. 9show the performance when the uplink load of the group of low frequency bands710a,710b,710cis not considered; hence only the second predetermined limit is considered when selecting the frequency location of the PCell. There is degradation in performance compared to using a frequency in the group of low frequency bands710a,710b,710cas PCell at low loads. One reason is that many wireless devices110a,110bhave limited power/SNR and therefore cannot make use of frequencies in the group of high frequency bands720a,720b,720c. This behavior is dominant at low uplink loads.