Method and arrangement for assisting a network management unit

TECHNICAL FIELD

0001Embodiments herein relate to a base station and a method in a base station. In particular, embodiments herein relate to assisting a network management unit in managing a cellular network.

BACKGROUND

0002In a typical cellular network, also referred to as a wireless communication system, User Equipments (UEs), communicate via a Radio Access Network (RAN) to one or more core networks (CNs).

0003A user equipment is a mobile terminal by which a subscriber can access services offered by an operator's core network. The user equipments may be for example communication devices such as mobile telephones, cellular telephones, or laptops with wireless capability. The user equipments may be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another mobile station or a server.

0004User equipments are enabled to communicate wirelessly in the cellular network. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between the user equipment and a server via the radio access network and possibly one or more core networks, comprised within the cellular network.

0005The cellular network covers a geographical area which is divided into cell areas. Each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also on cell size.

0006A cell is a geographical area where radio coverage is provided by the base station at a base station site on a specific radio frequency band using a specific radio access technology. One base station, situated on the base station site, may serve one or several cells covering non-overlapping, partly overlapping or completely overlapping geographical areas. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.

0007In some radio access networks, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).

0008In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to one or more core networks.

0009UMTS is a third generation, 3G, mobile communication system, which evolved from the second generation, 2G, mobile communication system GSM, and which is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.

0010According to 3GPP/GERAN, a user equipment has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. GERAN is an abbreviation for GSM EDGE Radio Access Network. EDGE is further an abbreviation for Enhanced Data rates for GSM Evolution.

0011In the context of this disclosure, a base station as described above will be referred to as a base station or a Radio Base Station (RBS). A user equipment as described above, will in this disclosure be referred to as a user equipment or a UE.

0012The expression DownLink (DL) will be used for the transmission path from the base station to the user equipment. The expression UpLink (UL) will be used for the transmission path in the opposite direction i.e. from the user equipment to the base station.

0013Cellular network operators have considerable effort in planning, configuring, optimizing, and maintaining their wireless access networks. These efforts may consume a great part of their Operational Expenditures (OPEX).

0014One important E-UTRAN requirement from the operators' side is hence a reduction in the cost for deployment, configuration, and optimization phases for the wireless access system. This may involve tasks for operating the cellular network, e.g., planning and verification. Today, operators resort to planning tools to dimension and plan their cellular networks according to a specific business strategy. The approach based on planning tools and prediction is, however, not fully accurate. Reasons for the inaccuracies are imperfections in the used geographic data, simplifications and approximations in the applied propagation models, and changes in the environment, e.g., construction and/or demolition or seasonal effects, i.e. foliage changes. Furthermore, changes in the traffic distribution and user profiles may lead to inaccurate prediction results.

0015The above mentioned shortcomings force operators to continuously optimize their cellular networks using measurements and statistics, and to perform drive test or walk tests. Drive test and walk tests provide a picture of the end user perception in the field and enables the operator to identify locations causing poor performance and their corresponding cause, e.g. incorrect tilt or handover settings. Drive test and walk tests, however, may only cover a limited part of the cellular network due to access restrictions and the cost and time involved. Further, only a snapshot in time of the conditions in the field is captured.

0016Hence, for network management purposes, a problem is that only a limited part of the cellular network may be analyzed.

0017Planning and verification for managing the cellular network may also be based on so called “measurement reports” from user equipments. In such reports the observed service quality may be reported to a network management unit within the cellular network. The triggering of the measurement report may either be periodic, event-triggered or event triggered periodic reporting. Periodic reporting may be initiated when the event occurs. Example of such events may be that an alternative cell is received at higher power levels compared to the serving cell, radio link failure, etc. Optionally, if available, these measurement reports may be tagged with an estimated mobile position. The standardization of such measurement reports is currently being carried out in 3GPP as Minimization of Drive-Tests (MDT).

0018However, the measurement reports are limited to reporting service quality measurements that are configured via the Radio Resource Control (RRC) measurement control and reporting procedures, such as Reference Symbol Received Power (RSRP) and Reference Symbol Received Quality (RSRQ), which are intended for mobility and other longer time scale radio resource mechanisms.

SUMMARY

0019In view of the discussion above, it is an object for embodiments herein to provide an improved way of assisting a network management unit in managing a cellular network.

0020According to a first aspect, the object is achieved by a method in a base station for assisting a network management unit in managing a cellular network. The base station is comprised in the cellular network. The base station determines a status of the cellular network. The status affects a measurement of a quality of a radio channel between the base station and a user equipment comprised in the cellular network. The measurement is to be performed by the user equipment. The base station receives a feedback report from the user equipment, which feedback report comprises the measurement of the quality of the radio channel between the base station and the user equipment. The base station evaluates a validity of the measurement based on the determined status. The base station sends a report to the network management unit. The report comprises an indication of the measurement and an indication of the validity, thereby assisting the network management unit in managing the cellular network.

0021According to a second aspect, the object is achieved by a base station for assisting a network management unit in managing a cellular network. The base station is comprised in the cellular network. The base station comprises a determination unit, configured to determine a status of the cellular network. The status affects a measurement of a quality of a radio channel between the base station and a user equipment comprised in the cellular network. The measurement is to be performed by the user equipment. The base station further comprises a receiver configured to receive a feedback report from the user equipment. The feedback report comprises the measurement of the quality of the radio channel between the base station and the user equipment. The base station further comprises an evaluation unit configured to evaluate a validity of the measurement based on the determined status. The base station further comprises a sending unit configured to send a report to the network management unit. The report comprises an indication of the measurement and an indication of the validity, thereby assisting the network management unit in managing the cellular network.

0022Tanks to embodiments herein, wherein the validity of a measurement comprised in a feedback report is evaluated, and by reporting an indication of the measurement and its validity to a network management unit, feedback measurements that are traditionally intended for scheduling and such short term tasks in the base station, may be used by the base station to assist the network management unit in managing the cellular network.

BRIEF DESCRIPTION OF THE DRAWINGS

0023<figref idref="DRAWINGS">FIG. 1</figref> is a schematic block diagram illustrating an embodiment of a cellular network.

0024<figref idref="DRAWINGS">FIG. 2</figref> is a schematic illustration of antenna port configurations in a base station.

0025<figref idref="DRAWINGS">FIG. 3</figref> is a combined signalling scheme and flowchart illustrating embodiments in a cellular network.

0026<figref idref="DRAWINGS">FIG. 4</figref> is a flowchart depicting embodiments of a method in a base station.

0027<figref idref="DRAWINGS">FIG. 5</figref> is a schematic block diagram illustrating embodiments of a base station.

DETAILED DESCRIPTION

0028Embodiments herein may be exemplified in the following non-limiting description of embodiments.

0029<figref idref="DRAWINGS">FIG. 1</figref> depicts a cellular network <b>100</b>. The cellular network <b>100</b> may be a LTE cellular network, a WCDMA cellular network, a GSM cellular network, any 3GPP cellular network, or any other cellular network. In this example, the cellular network is of LTE-type.

0030The cellular network <b>100</b> comprises a base station <b>105</b>. The base station <b>105</b> is in this example an eNB, but may in other embodiments be of another type and may in different embodiments be referred to by different names such as for example RBS, eNodeB, NodeB, B node, or BTS, depending on the technology and terminology used. The base station <b>105</b> may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station.

0031The cellular network <b>100</b> further comprises a user equipment <b>110</b>, which is located in a cell <b>115</b> served by the base station <b>105</b>.

0032The cellular network <b>100</b> further comprises a network management unit <b>120</b>. The network management unit <b>120</b> may be a physical network node or a logical network node. It may form part of the core network or the radio access network of the cellular network <b>100</b>. The network management unit may form an integrated part of for example the base station <b>105</b> or form part of another network node in the cellular network <b>100</b>, such for example a MME, a RNC, or a dedicated management node such as an Operation Support System, Network Management System or a computer dedicated to processing and analysing measurement data for network management purposes. In this example, the network management unit <b>120</b> is an Operation Support System node outside the radio access network and the core network.

0033The cellular network <b>100</b> further comprises two further base stations <b>125</b> serving two further cells <b>130</b>.

0034For the communication between the base station <b>105</b>, and the user equipment <b>110</b> to function properly, measurements are performed by the user equipment <b>110</b> and reported in so called user equipment feedback reports. These measurements are intended for short time scale radio resource mechanisms such as scheduling.

0035Scheduling may be performed by the base station <b>105</b> to allocate transmission resources such as subframes in a time domain, bandwidth in a frequency domain, and transmission layers in a spatial domain. The number of available transmission layers depends on the antenna configuration of the base station <b>105</b>. In this example, the base station <b>105</b> is equipped with four physical antenna ports. The reason for having more than one physical port may be Multiple Input Multiple Output (MIMO) support. The antenna ports may hence be used for transmission on a single antenna port to the user equipment <b>110</b>, transmission of diversity over several antenna ports to the user equipment <b>110</b> and/or spatial multiplexing over several antenna ports to the user equipment <b>110</b>.

0036In LTE Release 8 a cell may have 1, 2, or 4 physical antenna ports and different reference signals may be sent out on each of them.

0037<figref idref="DRAWINGS">FIG. 2</figref> illustrates the reference symbols per antenna port in LTE. In <figref idref="DRAWINGS">FIG. 2</figref>, each coordinate system schematically illustrates an example of a transmission layer, corresponding to an antenna port, and its available transmission resources, divided into so called resource blocks in the time and frequency domain. Each resource block groups several symbols over a time and frequency range, and typically contains one or several reference symbols. In <figref idref="DRAWINGS">FIG. 2</figref>, the reference symbols correspond to the filled squares. Note also that a reference symbol at one transmission layer may correspond to an empty symbol on other transmission layers to avoid interference from other transmission layers. The user equipment <b>110</b> may evaluate the received reference symbols and calculate feedback measurements.

0038The scope of these measurements may depend on a transmission mode of the user equipment <b>110</b>. In some modes, more feedback may be provided than in others. Hence, the feedback reports may comprise a variety of measurements, since the scheduling of transmissions between the base station <b>105</b> and the user equipment <b>110</b> may be based on a configurable amount of feedback information from the user equipment <b>110</b> and/or the base station <b>105</b>. In the following some example of feedback report measurements are described.

0039In the downlink, the user equipment <b>110</b> may report a Channel Quality Indicator (CQI), either frequency dependent across a fraction of, or across the entire, bandwidth, or averaged over a fraction or over the entire bandwidth. The user equipment <b>110</b> may also report a Rank Indicator (RI), informing about the estimated number of available transmission layers, i.e. antenna ports, and/or a preferred precoding matrix for spatial multiplexing.

0040In the uplink, the user equipment <b>110</b> may be requested to perform channel sounding, which means that it transmits known symbols using a specific power level over a fraction of, or over the entire, bandwidth. The base station <b>105</b> may then estimate the uplink path loss. For scheduling purposes, the base station <b>105</b> may also estimate the Signal to Interference and Noise Ratio (SINR) and determine a suitable transport format, for example a bit rate and the amount of code protection, for the allocated time-frequency resources. Such measurements in lower layers at the base station may also be considered as feedback reports, not from the UE but rather from the lower layer of the base station.

0041The feedback report measurements may be reported via Media Access Control (MAC), and are traditionally only intended for scheduling and other shorter time scale radio resource mechanisms in the user equipment and/or base station. Feedback report measurements are hence intended for a completely different use than the measurements comprised in the previously mentioned measurement reports, which are intended for mobility and other longer time scale radio resource mechanisms, and which are handled by the Radio Resource Control (RRC), and not by the MAC.

0042Embodiments herein are based on the understanding that the feedback report measurements may be rendered useful for a different purpose than scheduling and the like, namely for network management such as spatial performance data aggregation in the network management unit <b>120</b>. Embodiments herein are also based on the understanding that these feedback measurements, being traditionally intended for other purposes, may critically depend on settings, or statuses, in the cellular network <b>100</b> that may make them difficult to interpret, unsuitable, or even misleading, for network management purposes in the network management unit <b>120</b>.

0043Thanks to embodiments herein, feedback report measurements, which are typically handled via a Media Access Control (MAC) in the user equipment <b>110</b> and/or the base station <b>105</b>, may hence form the basis for a method in the base station <b>105</b> for assisting the network management unit <b>120</b> in managing the cellular network <b>100</b>.

0044<figref idref="DRAWINGS">FIG. 3</figref> is a combined flowchart and signalling scheme, illustrating how a method in the base station <b>105</b> for assisting the network management unit <b>120</b> in managing the cellular network <b>100</b> according to some embodiments herein may be implemented.

0045In action <b>301</b>, the base station <b>105</b> determines a status of the cellular network <b>100</b>. The status is in this example the number of antenna ports that the base station <b>105</b> uses. In this example, the base station <b>105</b> has disabled three out of four antenna ports for energy saving reasons. This is sometimes referred to as “antenna muting”, and is a method to reduce energy consumption in LTE Release 8, for example when the traffic is low in a cell.

0046In this disclosure, “cellular network status” and “status of the cellular network” may refer to for example one or more of a setting in the base station, such as the above described antenna configuration, but also to a radio situation or performance known to the base station <b>105</b>, such as an interference level, or a throughput, or a scheduling, etc., as will be described later in this document.

0047In action <b>302</b>, the user equipment <b>110</b> performs a measurement to estimate the number of antenna ports of the base station <b>105</b>. In this example, the user equipment <b>110</b> correctly estimates the number of antenna ports to one port.

0048The cellular network <b>100</b> being of LTE-type in this example, the user equipment <b>105</b> determines the number of antenna ports supported in the cell <b>115</b> by decoding the Physical Broadcast CHannel (PBCH). The number of antenna ports is not explicitly signaled on the PBCH and hence, it may not be changed without a complete re-start of the cell. Since the LTE Release <b>8</b> standard stipulates that the Physical Downlink Shared CHannel (PDSCH) shall use the same antenna ports as the PBCH, the user equipment <b>105</b> may already know the number of antenna ports once it has succeeded in decoding the PBCH properly. The user equipment <b>110</b> may then determine the number of antenna ports that the cell <b>115</b> supports once, and after that the user equipment <b>110</b> may not re-evaluate this decision.

0049In action <b>303</b>, the user equipment <b>110</b> sends a feedback report comprising the number of transmission layers that it has estimated in the received MIMO channel, i.e. “1” in this example. This feedback measurement is, as previously mentioned, referred to as the rank indicator.

0050The feedback report also comprises a measurement of the channel quality of the downlink. This feedback measurement is, as also previously described, referred to as the channel quality indicator.

0051In action <b>304</b>, the base station <b>105</b> receives, e.g. via the MAC, the feedback report with the rank indicator and the channel quality indicator measured by the user equipment <b>110</b>. The base station <b>105</b> may use this information in a traditional way such as in a feedback loop to disclose a suitable transmission format and a suitable number of independent data streams to send over the transmission layers for subsequent transmissions.

0052In action <b>305</b>, the user equipment <b>110</b> performs traditional performance measurements, such as RSRP and RSRQ, and reports these, via the RRC, in a so called measurement report, as previously described.

0053In action <b>306</b>, the base station <b>105</b> evaluates a validity of the reported rank indicator measurement by relating it to the antenna configuration status. In this example, it is concluded that the reported rank indicator may be ambiguous, since three antenna ports were disabled when the measurement was performed by the user equipment <b>110</b>. Hence, the measured rank “1” might be misleading for network management purposes if reported by itself, since it might be interpreted as if three channels out of four experienced severe fading dips, and therefore could not be recognized by the user equipment <b>110</b>. In a similar example, the four antenna ports are added together and transmitted over one antenna. Hence, the measured rank “1” might be misleading for network management purposes if reported by itself, since it might be interpreted as if the four antenna ports are fully correlated and therefore may not be used for individual streams, and are therefore recognized by the user equipment <b>110</b> as a rank 1 channel.

0054In action <b>307</b>, the base station <b>105</b> further evaluates the channel quality measurement. To do this, the base station <b>105</b> determines a further status in the cellular network <b>100</b>, which in this case is a status of the subframe during which the channel quality was measured by the user equipment <b>110</b>. If it is determined that the subframe in question was a so called “almost blank subframe” and/or if the subframe was an allocated subframe for the user equipment <b>110</b>, this status indicates that the measurement has a higher validity than a subframe during which interference is likely to have been more severe. By “almost blank subframe” is understood a subframe during which no other base stations, such as the further base stations <b>125</b> in <figref idref="DRAWINGS">FIG. 1</figref>, in the vicinity have scheduled transmissions that may interfere with the transmission in question. In this example, it is concluded that the channel quality measurement has high validity since it was indeed measured during an almost blank subframe.

0055In action <b>308</b>, the base station <b>105</b> reports the channel quality measurement together with an indication of its high validity to the network management unit <b>120</b>.

0056In this action the base station may also report the rank indicator as “full rank”, which is an indication both of the rank indicator itself and of its validity.

0057In another embodiment, the estimated number of antenna ports and the true number of antenna ports may be explicitly reported. In another embodiment, the rank indicator may simply be removed from the report due to the ports being disabled and the validity hence being regarded as too low.

0058Thanks to the report, the network management unit <b>120</b> is assisted in managing the cellular network <b>100</b>, since it may for example be used to aggregate spatial performance data from the location of the user equipment <b>110</b>.

0059In this example, the report is added to the measurement report and is further reported to the network management node. This may be an effective way of performing the reporting, since such measurement reports are intended for mobility and other longer time scale radio resource mechanisms, and may thus be sent to the network management unit <b>120</b> anyway. The user equipment measurement reports aim at giving relevant information about the radio network performance, and may also, as previously mentioned, comprise position tagging. By adding the indication of the feedback measurements and their validity to these measurement reports, the network management may be further facilitated. In other embodiments, an indication of the feedback measurement and its validity may be separately reported to the network management unit <b>120</b>.

0060In the following, further embodiments herein, relating to a method in the base station <b>105</b> for assisting the network management unit <b>120</b> in managing the cellular network <b>100</b> will be described with reference to the flowchart depicted in <figref idref="DRAWINGS">FIG. 4</figref>. As previously mentioned, the base station is comprised in the cellular network <b>100</b>, and may be of any of the above, in relation to <figref idref="DRAWINGS">FIGS. 1-3</figref>, described types.

0061The method comprises the following actions, which actions may be taken in any suitable order:

Action

401

0062In this action, the base station <b>105</b> determines a status of the cellular network <b>100</b>. The status affects a measurement of a quality of a radio channel between the base station and a user equipment <b>110</b> comprised in the cellular network <b>100</b>. The measurement is to be performed by the user equipment <b>110</b>.

0063The measurement may be a rank indicator or a channel quality indicator or a power headroom.

Action

402

0064In this action, the base station <b>105</b> receives a feedback report from the user equipment <b>110</b>, which feedback report comprises the measurement of the quality of the radio channel between the base station <b>105</b> and the user equipment <b>110</b>.

0065According to some embodiments, the base station <b>105</b> further receives from the user equipment <b>110</b> a further measurement of the radio quality.

Action

403

0066In this action, the base station <b>105</b> evaluates a validity of the measurement based on the determined status.

0067In some embodiments, the evaluating comprises relating the measurement to an antenna port configuration status or an interference status, or a subframe allocation status, or a receiver sensitivity status.

0068According to some embodiments, the radio channel is a downlink radio channel, the measurement is a rank indicator of the downlink radio channel, and the status is an antenna port configuration of the base station <b>105</b>. The evaluating may then comprise determining a maximum rank based on the antenna port configuration and relating the rank indicator to the maximum rank.

0069According to some embodiments, the radio channel is a downlink radio channel, and the measurement is a channel quality indicator measured over a subframe of the downlink radio channel. The evaluating may then comprise relating the channel quality indicator measurement to an interference level of the subframe, and/or to a presence of non-orthogonal downlink signals on the subframe, and/or to if the subframe is an allocated subframe for the user equipment <b>110</b>, and/or if the subframe is an almost blank subframe.

0070According to some embodiments, the radio channel is an uplink radio channel, and the measurement is a power headroom. The evaluating may then comprise relating the power headroom measurement to an interference level of the uplink radio channel or to an uplink receiver sensitivity at the base station <b>105</b>.

Action

404

0071In this action, the base station <b>105</b> sends a report to the network management unit <b>120</b>. The report comprises an indication of the measurement and an indication of the validity, thereby assisting the network management unit <b>120</b> in managing the cellular network <b>100</b>.

0072According to some embodiments, the indication of the measurement and/or the indication of the validity is the measurement itself. For example, in some embodiments, only measurements which at the evaluation in action <b>403</b> are evaluated to be of at least a certain validity may be reported. According to some embodiments, the report is sent as part of a measurement report.

0073Due to the relatively short user equipment feedback report time scale, a multitude of user equipment feedback reports together with associated cellular network status may be considered in the evaluation <b>403</b> and/or reporting <b>404</b>.

0074According to some embodiments, the base station <b>105</b> further receives from the user equipment <b>110</b> a further measurement of the radio quality, as previously mentioned in relation to action <b>402</b>. The evaluation may then be further based on the further measurement. It is possible that the user equipment feedback reports are more frequent than the user equipment measurement reports. This means that there might be a multitude of user equipment feedback reports and associated cellular network statuses available since the last user equipment measurement report. In such embodiments, but also in other embodiments where the report is not sent as part of a measurement report, the several feedback measurements may according to different embodiments herein be handled and combined in a number of different ways in the evaluation in action <b>403</b>, and in the reporting in action <b>404</b>, examples of which ways are listed below:

0075Only the most recent user equipment feedback report and associated cellular network status may be considered.

0076The user equipment feedback reports and associated cellular network status since the previous report may be averaged.

0077Only the worst case user equipment feedback report and associated cellular network status may be considered.

0078Only the median user equipment feedback report and associated cellular network status may be considered.

0079Only a percentile of user equipment feedback reports and associated cellular network status may be considered.

0080Only the majority vote of the user equipment feedback reports and associated cellular network statuses may be considered. For example, if the rank indicators 2,2,2,2,2,3,3,2,2 are stored since the last report, and the base station <b>105</b> has had 4 antenna ports transmitted during this period of time, the rank indicator 2 out of 4 may be reported.

0081The management system in LTE comprises Node Elements (NE) in the form of eNodeB. These are managed by a Domain Manager (DM), also referred to as the Operation and Support System (OSS). A DM may further be managed by a Network Manager (NM). Two NEs may inter-connect using the X2 interface, or via the MME using S1 interfaces, whereas the interface between two DMs is referred to as Itf-P2P. Functions that automatically optimize NE parameters may execute in the NE, DM, or the NMS. Hence, the network management unit <b>120</b> may be a physical or logical node which may form part of one or more of the entities comprised in the management system. The term “cellular network” should hence not be taken as limiting in the sense that the network management unit <b>120</b> may form part of a core network in some embodiments, and the reports may be sent from the base station over land line or over radio link.

0082In the following, feedback report measurements which may be relevant for various embodiments herein are described in more detail, along with descriptions of possible statuses of the cellular network <b>100</b> that may affect one or more of the measurements. The following measurements and statuses may hence be taken into consideration in action <b>401</b> when the status is determined, and/or in action <b>403</b> when the validity of the measurement is evaluated.

Rank Indicator

0083The rank indication measurement from the user equipment <b>110</b> provides information about the channel rank, that is the number of layers or streams that may be be used for DL transmission. Hence, the rank indicator feedback from the user equipment <b>110</b> informs the base station <b>105</b> about the estimated number of available transmission layers for spatial multiplexing. A low rank may indicate that the dispersiveness of the radio channel is low, and that the MIMO potential is limited. However, a low rank may also be due to the fact that the base station <b>105</b> has muted one of several antenna ports, as previously described. There are also several possible antenna configuration statuses that may be relevant for evaluating the validity of a rank indication measurement. For example, one or more physical antenna ports may be muted, and one or more virtual antenna ports may be added, and/or one or more sum signals from several antenna ports may be transmitted. In some embodiments, different virtual antenna ports may be added with various possibly pseudo random combination weights. The validity of a rank indication may therefore be evaluated in comparison to the maximum rank, which depends on the number of transmitted antenna ports. If the rank is equal to the number of antenna ports, then the channel may be referred to as being of “full rank”.

Precoding Matrix Indication

0084This measurement from the user equipment <b>110</b> informs the base station <b>105</b> about which precoding matrix that may be the most suitable for downlink communication, or an indicator of a suitable precoding matrix that may maximize the number of available transmission layers, or antenna ports. For this purpose, the user equipment <b>110</b> may essentially evaluate a list of possible precoding matrices, and select the most favorable one. The validity may depend on the number of available antenna ports. If some of them are muted or combined, then the interpretation of the precoding matrix indication should be done with consideration of the antenna port configuration.

Power Headroom

0085Power headroom measurements address the uplink power situation relative the maximum transmitter power level. Insufficient power headroom may indicate that the uplink coverage is insufficient. However, it may also depend on the interference contribution at the uplink receiver. Therefore, the power headroom may be adjusted to correspond to a nominal interference level, instead of the actual interference level. It may also depend on the required signal to interference and noise ratio for the assigned transport format. Therefore, the power headroom may be adjusted to correspond to a nominal signal to interference and noise ratio level.

0086Insufficient power headroom may also trigger initiation of uplink channel sounding to enable the base station <b>105</b>, to report uplink path gain estimates.

Uplink Channel Quality Indicators

0087Channel-quality indication measurements represent the recommended modulation scheme and coding rate that should be used for DL transmissions. The user equipment <b>110</b> may report CQI for either a fraction of, or for the entire, frequency band, either with frequency resolution or aggregated over a fraction or the entire frequency band.

0088The validity, or relevance, of the CQI may depend on whether the user equipment <b>110</b> is (re-)assigned resources depending on reported channel quality, and if the user equipment <b>110</b> is only reporting channel quality for assigned resources and/or on whether the base station <b>105</b> is aware of significant downlink interference contributions. For example, the base station <b>105</b> may be aware of non-orthogonal downlink signals that results in downlink interference. CQIs considered to be irrelevant at evaluation may be omitted from the reports.

0089According to some embodiments herein, the base station <b>105</b> may consider user equipment feedback report measurements and cellular network cellular network statuses such as for example the following: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0090">Feedback measurement in the form of a rank indicator, and the cellular network status in the form of a number of transmitted antenna ports.</li><li id="ul0002-0002" num="0091">Feedback measurement in the form of a precoding matrix indicator, and the cellular network status in the form of associated user equipment scheduling.</li><li id="ul0002-0003" num="0092">Feedback measurement in the form of an uplink power information and the cellular network status in the form uplink receiver sensitivity information. The uplink sensitivity information may be uplink interference and/or information about whether the uplink receiver combines a multitude of uplink transmissions before decoding.</li><li id="ul0002-0004" num="0093">Feedback measurement in the form of a channel quality indicator and the cellular network status in the form of base station power information.</li><li id="ul0002-0005" num="0094">Feedback measurement in the form of a channel quality indicator and the cellular network status in the form of base station scheduling information.</li></ul></li></ul>

0095The user equipment measurement reports give relevant information about the radio network performance. Together with position tagging, this may be used to aggregate spatial performance information. However, the user equipment measurement report scope is limited. According to some embodiments herein, the measurement reports are enriched by the base station combining user equipment feedback report measurements with relevant cellular network status.

0096Hence, according to various embodiments herein, the base station <b>105</b> assists the network management unit <b>120</b> in managing the cellular network <b>100</b>, by providing

0097accurate rank information considering eNB antenna power muting

0098accurate uplink power headroom information considering uplink receiver sensitivity

0099accurate channel quality information considering base station power information and/or scheduling information.

0100To perform the actions above for assisting the network management unit <b>120</b> in managing the cellular network <b>100</b>, the base station <b>105</b> comprises an arrangement schematically depicted in <figref idref="DRAWINGS">FIG. 5</figref>.

0101The term “configured to” used herein may also be referred to as “arranged to”.

0102As previously mentioned, the base station <b>105</b> is comprised in the cellular network <b>100</b>.

0103The base station <b>105</b> comprises a determination unit <b>500</b>. The determination unit <b>500</b> is configured to determine a status of the cellular network <b>100</b>. The status affects a measurement of a quality of a radio channel between the base station and the user equipment <b>110</b> comprised in the cellular network <b>100</b>. The measurement is to be performed by the user equipment <b>110</b>.

0104The measurement may be a rank indicator or a channel quality indicator or a power headroom.

0105The base station <b>105</b> further comprises a receiver <b>510</b>. The receiver <b>510</b> is configured to receive a feedback report from the user equipment <b>110</b>. The feedback report comprises the measurement of the quality of the radio channel between the base station <b>105</b> and the user equipment <b>110</b>.

0106The base station <b>105</b> further comprises an evaluation unit <b>520</b>. The evaluation unit <b>520</b> is configured to evaluate a validity of the measurement based on the determined status.

0107According to some embodiments, the evaluation unit <b>520</b> is configured to relate the measurement to an antenna port configuration status or an interference status, or a subframe allocation status, or a receiver sensitivity status.

0108According to some embodiments, the radio channel is a downlink radio channel, the measurement is a rank indicator of the downlink radio channel, and the status is an antenna port configuration of the base station <b>105</b>. The evaluation unit <b>520</b> may then further be configured to determine a maximum rank based on the antenna port configuration and relating the rank indicator to the maximum rank.

0109According to some embodiments, the radio channel is a downlink radio channel and the measurement is a channel quality indicator measured over a subframe of the downlink radio channel. The evaluation unit <b>520</b> may then further be configured to relate the channel quality indicator measurement to an interference level of the subframe, and/or to a presence of non-orthogonal downlink signals on the subframe, and/or to if the subframe is an allocated subframe for the user equipment <b>110</b>, and/or if the subframe is an almost blank subframe.

0110According to some embodiments, the radio channel is an uplink radio channel and the measurement is a power headroom. The evaluation unit <b>520</b> may then further be configured to relate the power headroom measurement to an interference level of the uplink radio channel or to an uplink receiver sensitivity at the base station <b>105</b>.

0111The base station <b>105</b> further comprises a sending unit <b>530</b>. The sending unit <b>530</b> is configured to send a report to the network management unit <b>120</b>. The report comprises an indication of the measurement and an indication of the validity, thereby assisting the network management unit <b>120</b> in managing the cellular network <b>100</b>.

0112The sending unit <b>530</b> may further be configured to send the report as part of a measurement report.

0113The embodiments of the base station <b>105</b> for assisting the network management unit <b>120</b> in managing the cellular network <b>100</b> may be implemented through one or more processors, such as a processor <b>540</b> in the base station <b>105</b> depicted in <figref idref="DRAWINGS">FIG. 5</figref>, together with computer program code for performing the actions of embodiments herein.

0114The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the base station <b>105</b>.

0115One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the base station <b>105</b> e.g. remotely.

0116The base station <b>105</b> may further comprise a memory <b>550</b> comprising one or more memory units. The memory <b>550</b> may be arranged to be used to store data such as for example status information, one or more feedback reports and/or measurements. It may further be arranged to store applications to perform the actions of the embodiments herein when being executed in the base station <b>105</b>.

0117The embodiments are not limited to the above-described embodiments. Various alternatives, modifications and equivalents may be used.

0118When using the word “comprise” or “comprising” it shall be interpreted as non-limiting, i.e. meaning “consist at least of”.

0119The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.