MODE

TECHNICAL FIELD

The present invention generally relates to a method in a radio base station of a wireless communications network and to a radio base station itself, more particularly to a method of selecting a channel quality reporting mode for reporting estimated channel quality and to a radio base station adapted to select a channel quality reporting mode.

BACKGROUND

Long Term Evolution (LTE) is a step in the development of Universal Mobile Telecommunications System (UMTS) beyond the original 3rd generation Wideband Code Division Multiple Access (WCDMA) radio access technology. LTE comprises a new radio interface and a new radio access network architecture. LTE is also known as the Evolved Universal Terrestrial Radio Access (E-UTRA) standard, as promulgated by the Third Generation Partnership Project (3GPP). In one of the E-UTRA standard technical specifications 3GPP TS 36.213, entitled: "3 ^rd generation Partnership Project; Technical Specification Radio Access Network E-UTRA; Physical Layer procedures ' ^' , there are defined four reporting modes for use on a Physical Uplink Control Channel (PUCCH) and five reporting modes for use on a Physical Uplink Shared Channel (PUSCH). The above mentioned standard further defines seven different transmission modes denoted transmission mode i, where i=l ,2, ...,7. For each transmission mode i, it is specified e.g. which antenna port(s) than can be used. Note however that additional configuration parameters, other than which antenna port(s) is/are used, are also specified e.g. which Downlink Control Information (DCI) format and which "Search Space" to be used.

The reporting modes, which are generally used to report estimated channel conditions, can be considered as recommendations, sent as feedback by a User Equipment (UE), on what transmission configuration and related parameters the network should use if/when transmitting to the UE. The UE typically determines these recommendations based on estimates of the instantaneous downlink channel conditions/quality. The recommendations include one or several pieces of information such as a Rank Indicator (RI), a Precoder Matrix Indicator (PMI) and a Channel Quality Indicator (CQI).

Thus, the RI, the PMI, and the CQI, may, in different combinations and depending on a configuration form a reporting mode.

The RI provides information about channel rank or, expressed differently, a number of useful transmission layers used for downlink transmission to a UE. As an example, RI only needs to be reported when the UE is in a spatial-multiplexing reporting mode.

The PMI is defined as a signal fed back by a UE to support Multiple Input Multiple-Output (MIMO) operation, and provides a precoder matrix (within a codebook shared by the UE and eNodeB) used for downlink transmission. Similarly to the RI, the PMI is only reported if a UE is configured when the UE is in a spatial-multiplexing reporting mode. The CQI comprises a recommended modulation scheme and a recommended coding rate used for downlink transmission, usually based on a received downlink Signal to Interference Noise Ratio (SINR), i.e. downlink radio channel quality as experienced by the UE, and knowledge of the UE ^' s receiver characteristics.

The reporting modes are, for each UE, individually configured using Radio Resource Control (RRC) signaling. There are typically, for a UE, defined one PUCCH reporting mode and one PUSCH reporting mode at the same time. The reporting of e.g. channel state (or status) information on PUCCH according to a PUCCH reporting mode is performed with a fixed interval (i.e. periodically) unless the UE is scheduled one or more PUSCH resources on the PUCCH reporting instance, because then the channel state (or status) information which should have been reported on PUCCH is reported on PUSCH instead.. Reporting of channel state (or status) information on PUSCH according to a PUSCH reporting mode is performed when the eNodeB so requests.

Figure la represents, according to the previously described technical specifications, CQI and PMI feedback types for how the UE, which is semi-statically configured by higher layers, is to be configured to feed back CQI and PMI and corresponding RI (not denoted in Figure la) on the same PUSCH using one of the reporting modes given in the figure. The feedback types are based on categorizations of channel status reports. A PUSCH CQI feedback type reflects if the CQI is a wideband CQI or a subband CQI. A wideband report reflects the status over an entire cell bandwidth whereas a subband report reflects the status over each subband. It should be mentioned that each subband comprises one or a plurality of subcarriers, usually associated with frequency selectivity. A subband CQI report can be a UE selected subband CQI report or a higher layer configured subband CQI report. A PMI feedback type defines different PMI types to be used in combination with a PUSCH CQI feedback type. Three PMI scenarios are defined: no PMI; single PMI and multiple PMI. Multiple PMI means that the UE should select a preferred precoding matrix from a codebook subset per subband. As an example, Mode 1-2 means that wideband CQI is used together with multiple PMI. Mode 3-0 means that higher layer-configured subband CQI is used together with no PMI. Note that all combinations of CQI and PMI are not available, for example there is no PUSCH Mode 3-2 defined with both higher layer-configured subband CQI and multiple PMI. For each reporting mode, the technical specifications disclose a mode description.

Figure lb represents CQI and PMI feedback types for PUCCH reporting modes. The reporting modes include different CQI and PMI feedback types, as mentioned above. Note however that for PUCCH, there is no multiple PMI and there is no higher layer-configured subband CQI type. However, reporting Mode 2-0 exists for both PUSCH and PUCCH reporting, as can be seen in the figures la and lb, meaning that UE selected subband CQI with no PMI can be selected both for PUSCH and PUCCH reporting.

Figure 2 illustrates a signaling scheme involving a radio base station (denoted a eNodeB or eNB in LTE) and a UE for enabling the UE to use a reporting mode, according to prior art. As shown, the eNodeB broadcasts system information using R C signaling. The UE entering a cell served by the eNodeB reads broadcasted system information and sends a message including a Media Access Control Random Access CHannel preamble (MAC RACH preamble). The eNodeB receives the MAC RACH preamble message and sends a MAC RACH response to the UE, the response including resource allocation information for scheduling an uplink transmission. The UE connects to the cell and, using RRC signaling, sends a RRC connection request and in response to the request gets RRC connection setup including configuration information including information on what reporting mode the UE is to use in the cell. The UE configures it settings and reports to eNodeB, and then the UE starts sending reports on estimated channel quality according to the reporting mode. The reporting mode is generally determined upon initial configuration of the eNodeB.

As described earlier, the technical specifications only specify the reporting modes that are to be used to feed back CQI and PMI and corresponding RI. It is however not specified under what conditions to use which reporting mode. This also means that it is not specified how to determine which reporting mode is most suitable to use by the UE.

SUMMARY

An object of an exemplary embodiments of the present invention is thus to provide a radio base station and a method in a radio base station, of selecting a channel quality reporting mode from a list of predefined channel quality reporting modes, that is most suitable for use by a UE.

According to an aspect of exemplary embodiments of the present invention, there is provided a method of selecting a channel quality reporting mode from a list of predefined channel quality reporting modes, in a radio base station serving a cell in a wireless communications network. The method comprises: measuring a traffic load in the cell; comparing the measured traffic load with a predefined threshold; using the result from the comparison to select a channel quality reporting mode; and sending configuration information to a UE, informing the UE of the channel quality reporting mode to use for reporting channel quality estimations of a communication channel set up between the radio base station and the UE. According to another aspect of exemplary embodiments of the present invention, there is provided a radio base station, being adapted to serve a cell in a wireless communications network, for selecting a channel quality reporting mode from a list of predefined channel quality reporting modes. The radio base station comprises: a measurement unit adapted to measure a traffic load in the cell; a comparator unit adapted to compare the measured traffic load with a predefined threshold, a selector unit adapted to select a channel quality reporting mode based on a result from the comparison; and a transceiver adapted to send configuration information to a UE to inform the UE of the channel quality reporting mode to use for reporting channel quality estimations of a communication channel set up between the radio base station and the UE. An advantage of the exemplary embodiments of the present invention is that cell performance is improved due to that a most suitable channel quality reporting mode is selected.

Another advantage of the exemplary embodiments of the present invention is that control signaling overhead is decreased in the cell. Another advantage of the exemplary embodiments of the present invention is that selection of a channel quality reporting mode is self configurable and thereby simplified.

Still other advantages, objects and features of the embodiments of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawings, attention to be called to the fact, however, that the following drawings are illustrative only, and that various modifications and changes may be made in the specific embodiments illustrated as described within the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la illustrates representation of CQI and PMI feedback types for PUSCH reporting modes according to prior art.

Figure lb illustrates representation of CQI and PMI feedback types for PUCCH reporting modes according to prior art.

Figure 2 is a signaling scheme illustrating an implementation of UE configuration according to prior art. Figure 3 is a signaling scheme illustrating a method of selecting a channel quality reporting mode according to an exemplary embodiment of the present invention.

Figure 4 is a signaling scheme illustrating a method of selecting a channel quality reporting mode according to another exemplary embodiment of the present invention.

Figure 5 is a signaling scheme illustrating a method of selecting of a channel quality reporting mode according to yet another exemplary embodiment of the present invention.

Figure 6 is an example illustrating throughput gain of exemplary reporting modes vs. traffic load. Figure 7 is a block diagram illustrating a radio base station, in a wireless communications network, according to an exemplary embodiment of the present invention.

Figure 8 is a block diagram illustrating a radio base station, in a wireless communications network, according to another exemplary embodiment of the present invention. Figure 9A is a simulation result illustrating cell throughput in relation to mean user throughput in a exemplary 2x2 MIMO system.

Figure 9B is a simulation result illustrating cell throughput in relation to 5% user throughput in a exemplary 2x2 MIMO system.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, scenarios, techniques, etc. in order to provide thorough understanding of the present invention. However, it will be apparent from the following that the present invention and its embodiments may be practiced in other embodiments that depart from these specific details. The exemplary embodiments of the present invention are described herein by way of reference to particular example scenarios. In particular the invention is described in a non-limiting general context in relation an LTE system.

Figure 3 is a signaling scheme illustrating a method of selecting a channel quality reporting mode according to exemplary embodiments of the present invention. As shown, a radio base station (e.g. eNodeB) 100 broadcasts system information using RRC signaling. A UE 120 entering a cell served by the eNodeB 100 reads the broadcasted system information and then sends a message including a MAC RACH preamble. The eNodeB 100, upon receiving the MAC RACH preamble message, sends a MAC RACH response including resource allocation information for scheduling an uplink transmission. When the UE 120 receives the MAC RACH response, it then connects to the cell and sends a RRC connection request to the eNodeB 100. Upon receiving the request, the eNodeB 100, according to the exemplary embodiments of the present invention, starts measuring (SI) a traffic load in the cell and then compares (S2) the measured traffic load with a predefined threshold to determine if a certain condition is fulfilled or not. Example of a condition is that traffic load in the cell exceeds or not a defined threshold. Another example of condition is that the number of UEs in the cell exceeds or not a defined threshold. If the comparison results in that the threshold is not exceeded for a certain measure of a cell characteristic, a channel quality reporting mode is selected (S3) from a list of predefined channel quality reporting modes known to the eNodeB 100. However, if the threshold is exceeded, another channel quality reporting mode is selected (S3) from the list. It should be noted that the threshold is predefined according to several tests performed in the cell, such as for example tests of throughput in relation to traffic load.

Thus depending on the result from the comparison a channel quality reporting mode is selected.

Referring back to figure 3, when the eNodeB 100 has selected the channel quality reporting mode, the eNodeB then sends (S4) configuration information to the UE using RRC signaling, informing the UE 120 of the selected channel quality reporting mode.

In an exemplary embodiment, the (S4) configuration information can be sent together with other basic information, such as scrambling code, resource blocks for use, although this is not necessary.

It should be noted that the eNodeB 100 may be configured to include the (S4) configuration information in a RRC connection response as a response to the RRC connection request during a setting up of a communication channel between the eNodeB 100 and the UE 120. Referring back to figure 3, when the (S4) configuration information is received by the UE 120, the UE configures it settings based on the channel quality reporting mode indicated in the (S4) configuration information. Thereafter, the UE 120 sends a RRC connection setup complete completing the setting up of a communication channel between the UE 120 and the eNodeB 100. The UE 120 then starts reporting channel quality estimations of the set up communication channel according to the selected reporting mode.

These reports are e.g. used by the eNodeB 100 for link adaptation and resource scheduling.

According to an exemplary embodiment of the present invention, the report(s) including channel quality estimations is/are sent as part of channel state information, CSI, report(s). This is the case, for example, in a MIMO system wherein CSI is reported by a UE. This CSI report may include the above mentioned CQI, the PMI, and the RI indicating the number of independent channels. It should be mentioned that the report(s) including channel quality estimations are sent periodically or a-periodically over the PUCCH and/or the PUSCH. In other words, the reports are sent periodically on PUCCH (or on PUSCH if the UE is scheduled a PUSCH resource at a PUCCH reporting instance) or a-periodically on PUSCH Comparing with the prior art solution where a static or fixed channel quality reporting mode configuration is used without taking into consideration the traffic load in the cell, the exemplary embodiments of the present invention instead selects the most suitable channel quality reporting mode based on the actual traffic load in the cell. This leads to that a decrease of control signaling overhead in the cell is achieved. As an example, if the channel quality reporting mode Mode 3-1 corresponding to "Higher- layer configured (subband CQI) with single PMI" (see figure la) is used for static configuration according to prior art, even though there is no gain in using Mode 3-1 , this will lead to unnecessary overhead on a Physical Downlink control Channel (PDCCH) where scheduling assignments are transmitted. It should be mentioned that subband (frequency selective) scheduling often mean that several scheduling assignments are transmitted in a PDCCH sub-frame. Unnecessary overhead is also a result when unused subband (frequency selective) CQI is reported on PUSCH.

By applying the teaching of the exemplary embodiments of the present invention wherein the most suitable channel quality reporting mode is selected based on the traffic load in the cell, unnecessary overhead is avoided and/or reduced because instead of selecting Mode 3-1 as in the example above, wideband CQI with multiple PMI (i.e. Mode 1-2) is instead selected. This may further give a link adaptation gain.

Referring to figure 4 there is illustrated a signaling scheme depicting a method of selecting a channel quality reporting mode according to another exemplary embodiment of the present invention. As shown, the signalling flows used up to the RRC connection request transmitted from the UE 120 to the eNodeB 100 are similar to the ones already described in conjunction with figure 3. However, according to this exemplary embodiment of the present invention, the eNodeB 100 is adapted to measure a traffic load in the cell corresponding to measurement of cell traffic load parameters (Sla) and/or corresponding to estimation of UE traffic load parameters (Sib).

According to an exemplary embodiment of the present invention, the cell traffic load parameters relate to one or more of: number of active UEs, downlink cell load, requested amount of resource blocks in downlink, physical control channel load factor, and on physical uplink control channel.

According to another exemplary embodiment of the present invention, the UE traffic load parameters comprise one or more of: UE traffic type (e.g. service type), UE group relation (e.g. UE category e.g. laptop, mobile phone, PDA, etc.), requested amount of downlink resource blocks, UE subscription information, and historical profile.

Referring back to figure 4, and according to an exemplary embodiment, the eNodeB 100 is adapted to (S2a) compare the cell traffic load parameters (Sla) with a predefined threshold respectively. According to another exemplary embodiment the eNodeB 100 is adapted to (S2b) compare the estimated UE traffic load parameters (Sib) with a predefined threshold respectively. Note however, that eNodeB 100 is adapted to perform both (S2a) and (S2b).

Each one of the above mentioned parameters is analyzed and compared with a respective predefined threshold in order to determine if a condition is achieved. The eNodeB 100 is further configured to (S3) select a channel quality reporting mode based on the result from the comparison.

As an exemplary embodiment, the eNodeB may select a channel quality reporting mode based on PDCCH and/or PUCCH capacity. If e.g. the PDCCH capacity is very limited, scheduling assignments can only be transmitted to a limited number of UEs. If e.g. the PUCCH capacity is limited, only a small number of UEs can be scheduled due to that a small number of available ACK/NACK (Acknowledgment/Non-Acknowledgment) responses can be transmitted from the small number of UEs. In these cases, the throughput gain achieved by using a subband CQI reporting mode is considered small and therefore, channel quality reporting mode corresponding to wideband CQI (i.e. Mode 1-2) is preferred.

Referring back to figure 4, when the eNodeB 100 has selected the channel quality reporting mode, the eNodeB then sends (S4) configuration information to the UE using RRC signaling, informing the UE 120 of the selected channel quality reporting mode.

It should be noted that the eNodeB 100 may be configured to include the (S4) configuration information in a RRC connection response as a response to the RRC connection request during a setting up of a communication channel between the eNodeB 100 and the UE 120. Referring back to figure 4, when the (S4) configuration information is received by the UE 120, the UE configures it settings based on the channel quality reporting mode indicated in the (S4) configuration information. Thereafter, the UE 120 sends a RRC connection setup complete completing the setting up of a communication channel between the UE 120 and the eNodeB 100. The UE 120 then starts reporting channel quality estimations of the set up communication channel according to the selected reporting mode.

For example, if the type of UEs in the cell served by the eNodeB, are mobile phones or if a majority of UEs generate voice traffic, then the selected channel quality reporting mode is Mode 1-2 (i.e. wideband CQI mode) because selection of a channel quality reporting mode corresponding to a subband CQI is considered to give less gain . If on the other hand the mobile category is laptop and/or the majority of the traffic generates high data rate, then subband CQI Mode 3-1 is preferably selected since a wideband CQI mode gives less gain in this scenario.

In yet another example, a UE traffic load parameter corresponding to a UE data priority is used as a basis for selecting a channel quality reporting mode. If there are a lot of other UEs in the cell with high resource demand and higher data priority and these other UEs are configured to use Mode 3-1, then the eNodeB could select the same mode i.e. Mode 3-1 for this UE. However, since the other UEs have high data priority and are maybe more resource demanding than this UE, the eNodeB would instead select another channel quality reporting mode e.g. Mode 1-2.

In yet another example, a UE traffic load parameter corresponding to a requested amount of downlink resource blocks is used as a basis for selecting a channel quality reporting mode. The eNodeB can, for example, calculate an average amount of downlink resource blocks as the number of resource blocks assigned to other (active) UEs in the cell with same data priority as the UE being configured, divided by the number of active UEs. This calculated amount is then compared to a predefined threshold and if the average amount of downlink resource blocks is smaller than this threshold, a PUSCH channel quality reporting mode is selected, for example Mode 3-1, otherwise another mode is selected e.g. Mode 1-2. Note however that after the setting up of the communication channel the eNodeB 100 is configured to measure the traffic load in the cell (i.e. cell traffic load and/or UE traffic load), and reselect a new channel quality reporting mode to a more suitable channel quality reporting mode when the eNodeB determines there is a gain in doing so. This is illustrated in figure 5 which is a continuation from figure 4 i.e. after the setting up of the communication channel between the eNodeB 100 and the UE 120 and after that the UE 120 has configured it settings according to the channel quality reporting mode (initially) selected by the eNodeB 100. As shown, the eNodeB 100 is adapted to measure (S5) a UE traffic load on the set up communication channel and then compares (S6) the measured UE traffic load with a threshold prior to selecting (S7) a new channel quality reporting mode as a result of the comparison.

It should be mentioned that if the eNodeB 100 (S8) reselects the same channel quality reporting mode as the previous one then there is no need for the eNodeB 100 to send a new configuration information to the UE 120 since the UE 120 already knows which mode to use.

However, if the eNodeB 100 (S8) selects a new channel quality reporting mode that differs from the initial one, the eNodeB 100 then sends (S9) new configuration information to the UE 120 informing the UE of the new channel quality reporting mode to use for enabling the UE to report channel quality estimations of the set up communication channel. Thereafter the UE updates it configuration settings and inform the eNodeB 100 of the same prior to start reporting according to the new channel quality reporting mode. Note that the selection of the channel quality reporting mode can be based on channel time variations, and/or frequency selectivity of the set up communication channel. Note also that CQI adjustment algorithms may also be considered when selecting a channel quality reporting mode. CQI adjustment algorithms can use a fixed Link Adaptation (LA) margin, or use a dynamic outer-loop CQI adjustment based on Hybrid Automatic Repeat reQuest (HARQ) information. The CQI adjustment algorithms could be applied for wideband or subband (frequency selective). A CQI adjustment algorithm could also be statically or semi-statically configured in the eNodeB.

Referring to figure 6, there is illustrated a throughput gain of exemplary channel quality reporting modes (PUSCH Mode 1-2 resp. PUSCH Mode 3-1) versus traffic load. In this example, the traffic load parameter that is used for determining which channel quality reporting mode is most suitable to select, is the cell load on downlink channel between a UE(s) (not shown) and a eNodeB (not shown). As shown, at low traffic load, PUSCH Mode 1-2 gives a higher throughput gain compared with using PUSCH Mode 3-1. But at high traffic load, PUSCH Mode 3-1 gives a higher throughput as compared to if PUSCH Mode 1-2 is used. By high traffic load is meant the scenario where the available bandwidth is shared among several UEs and each UE is scheduled a limited number of resources, whereas at low load more resources can be assigned/scheduled to UEs. As shown in figure 6, there is a switching point, denoted Th, where a load threshold can be set for selecting between the two channel quality reporting modes (PUSCH Mode 1-2 and PUSCH Mode 3-1). The load threshold Th is e.g. a design parameter determined based on simulation or tests and/or can be based on the scheduling principle that is used in the network. The threshold Th may also depend on other properties not explicitly described here. Note that figure 6 is only an example and the exemplary embodiments of the present invention are not restricted to the modes shown in this figure 6.

Figure 7 is a block diagram illustrating a radio base station 100 in a wireless communications network for selecting a channel quality reporting mode from a list of predefined channel quality reporting modes in accordance to an exemplary embodiment of the present invention. As shown, the radio base station 100 (denoted RBS) which can be a eNodeB of a LTE system, is as previously described configured to serve a cell 110 and to be in communication with a UE 120 in the cell 110. The RBS 100 comprises a measurement unit 101; a comparator unit 102; a selector unit 103 and a transceiver 104. The measurement unit 101 is adapted to measure a traffic load in the cell 110. This measurement(s) is/are either performed initially when setting up a communication with a UE 120 or at any time after having set up the communication channel with the UE 120. Additional details concerning the measurements that the RBS 100 is configured to performed have already been described earlier and are therefore not unnecessarily repeated. The comparator unit 102 is adapted to compare the measured traffic load in the cell with a predefined threshold and to determine whether the measured traffic load in the cell exceeds the predefined threshold or not. As mentioned earlier, the predefined threshold may be determined by making several tests and/or simulations and/or estimations in the cell and/or in the network to which the RBS 100 belongs to.

Referring back to figure 7, the selector unit 103 of RBS 100 is adapted to select a channel quality reporting mode based on a result from the comparison performed by the comparator unit 102. After selection of the (most suitable) channel quality reporting mode, the transceiver 104 of RBS 100 is adapted to send configuration information to the UE 120 to inform the UE of the channel quality reporting mode to use.

As mentioned earlier, the configuration information can be sent before a communication channel is set up between the UE 120 and the RBS 100 and/or be sent during the setting up of the communication channel. As described earlier, the UE 120, upon receiving the configuration information, configures it settings and uses the selected channel quality reporting mode, indicated in the configuration information, to report channel quality estimations of a set up communication channel.

Figure 8 is another block diagram illustrating a radio base station (RBS 100), in a wireless communications network, according to other exemplary embodiments of the present invention. As shown, the measurement unit 101 is here considered to comprise a first measurement sub-unit 101a adapted to measure traffic load in the cell corresponding to cell traffic load parameters relating to one or more of: number of active UEs, downlink cell load, requested amount of resource blocks in downlink, physical control channel load factor, and physical uplink control channel. The RBS 100 is also shown comprising a comparator unit 102 including a first comparator sub-unit 102a adapted to compare each of the cell traffic load parameters with a predefined threshold respectively.

The measurement unit 101 of the RBS 100 is also shown comprising a second measurement sub-unit 101b adapted to measure traffic load in the cell corresponding to estimated UE traffic load parameters, and the comparator unit 102 is shown further comprising a second comparator sub-unit 102b adapted to compare each of the estimated UE traffic load parameters with a predefined threshold respectively. The estimated UE traffic load parameters are one or more of: UE group relation, requested amount of downlink resource blocks, UE subscription information, UE type and historical profile. The measurement unit 101 of the RBS 100 is also shown comprising a third measurement sub-unit 101c which is adapted to measure a UE traffic load of a previously set up communication channel. The comparator unit 102 further comprises a third comparator sub- unit 102c adapted to compare each of the measured UE traffic load parameters of the set up communication channel with a predefined threshold respectively. Assuming that the UE 120 already have received a configuration information comprising an (initial) channel quality reporting mode, the selector unit 103 of RBS 100 is configured to select a new channel quality reporting mode based on the measured UE traffic load of the set up communication channel and/or based on new traffic load measurements and comparison with the predefined threshold. As shown in figure 8 and according to this exemplary embodiment of the present invention, the selector unit 130 is shown comprising a comparator circuit 103a configured to compare if the new reporting mode differs from the (initial) and/or stored channel quality reporting mode. If the selector unit 103 determines that the new reporting mode is different from the previously used, then the selector unit 103 is configured to inform the transceiver 104 to send new configuration information to the UE 120. Note that the comparator circuit 103a may be located within the transceiver 104 or within any other unit or part of RBS 100. According to an exemplary embodiment of the present invention, the selector unit 103 is further adapted to select a channel quality reporting mode based on channel time variations, and/or frequency selectivity of the set up communication channel. The transceiver 104 of the RBS 100 is further adapted to receive channel quality reports including channel quality estimations performed by the UE 120, and the selector unit 103 is further adapted to use the channel quality reports to enable a scheduler (not shown) of RBS 100 to channel-dependent schedule a downlink channel. The selector 103 is also configured to select a downlink transmission configuration in e.g. the LTE network.

Referring to figures 9A-9B, there are illustrated simulation results. Figure 9A depicts cell throughput in relation to mean user throughput in an exemplary 2x2 MIMO system. Figure 9B illustrates cell throughput in relation to 5% user throughput in an exemplary 2x2 MIMO system.

In the simulations, it was assumed full buffer traffic and also assumed a Non Line-of Sight (NLOS) channel model. During the simulations, the UEs reporting wideband CQI are using proportional fair in time domain (PFT) scheduling, while UEs reporting subband CQI are using proportional fair in time and frequency domain (PFTF) scheduling. The different channel quality reporting modes used during the simulations are indicated in the margin (PUCCH Mode 2-1, PUCCH Mode 1-1; PUSCH Mode 2-2; PUSCH Mode 3-1 and PUSCH Mode 1-2). From Figures 9A it can be seen that e.g. curve representing PUSCH Mode 3-1 intersects with the curve representing PUSCH Mode 2-2 when the served traffic (i.e. cell traffic load) is approximately 6,3 Mbps. Thus below 6.3 Mbps, it is most suitable to use PUSCH Mode 2-2 since the UE throughput is higher compared to if PUSCH Mode 3-1 is used. But if the cell traffic load is above 6.3 Mbps it is most suitable to use PUSCH Mode 3-1 since the UE throughput is higher compared to that if PUSCH 2-2 is used. Thus, it is clear that the exemplary threshold value of 6.3 Mbps can be used when selecting a most suitable channel quality reporting mode. Note however, that the exemplary embodiments of the present invention are neither restricted to this value of the threshold nor are they limited to the simulations shown in figure 9 A. From figure 9B representing cell throughput versus 5% user throughput, it can be seen that the curve representing PUSCH Mode 3-1 intersects with the curve representing PUSCH Mode 2-2 when the served traffic (i.e. cell traffic load) is approximately 7.5 Mbps. Thus below 6.3 Mbps, it is most suitable to use PUSCH Mode 2-2 since the 5% UE throughput is higher compared to if PUSCH Mode 3-1 is used. But if the cell traffic load is above 7.5 Mbps it is most suitable to use PUSCH Mode 3-1 since the 5% UE throughput is higher compared to that if PUSCH 2-2 is used. Thus, it is clear that the exemplary threshold value of 7.5 Mbps can be used when selecting a most suitable channel quality reporting mode. Note again that the exemplary embodiments of the present invention are neither restricted to this value of the threshold nor are they limited to the simulations shown in figure 9B. Note that the exemplary embodiments of the present invention are not restricted to a 2x2 MIMO system.

The present invention and its exemplary embodiments can be realized in many ways. For example one embodiment of the present invention includes a computer-usable or computer- readable medium comprising a computer program code configured to cause a processor or a computer to execute instructions stored thereon. The executable instructions perform the method steps of the exemplary embodiments of the present invention as previously described and as presented in the appended method claims.

While the invention has been described in terms of several preferred embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent upon reading of the specifications and upon study of the drawings. It is therefore intended that the following appended claims include such alternatives, modifications, permutations and equivalents as fall within the scope of the present invention.