Method and arrangement for signaling of parameters in a wireless network

Abstract

A mobile terminal receives, over a first cell configured on a carrier frequency, at least one parameter associated with a second cell configured on a carrier frequency. The at least one parameter comprises a cell identity. The mobile terminal then derives at least one physical layer characteristic for the second cell based on the received at least one parameter. Thereby, the mobile terminal is able to receive transmissions over the second cell, even if it could not initially detect the presence of the cell.

Claims

1. A method for signaling cell identity information in a wireless communications network, the method implemented by a user equipment (UE) configured to receive transmissions over first and second cells, wherein the second cell is configured on a carrier frequency based on a physical layer characteristic for the second cell, and wherein the physical layer characteristic is derived from one or more parameters received by the UE over the first cell, the method comprising: receiving, over the first cell, an indication that no cell-specific reference (CSR) signals are detectable in the second cell; and refraining from performing measurements on CSR signals in the second cell responsive to receiving the indication.

2. The method of claim 1 wherein the one or more parameters comprise information indicating a cell identity of the second cell, and a number of transmit antenna ports at the second cell.

3. The method of claim 1 further comprising receiving, over the first cell, an indication that the user equipment should use the one or more parameters received over a first cell to derive the at least one physical layer characteristic for the second cell.

4. The method of claim 1 wherein the at least one physical layer characteristic comprises one or more of: a scrambling code, a reference signal configuration, a control signaling configuration.

5. The method of claim 4 wherein the at least one physical layer characteristic comprises one or more of: a PUSCH scrambling code, a PDSCH scrambling code, a L1/L2 control signaling scrambling code.

6. The method of claim 4 wherein the at least one physical layer characteristic comprises one or more of: a cell-specific reference signal configuration, a sounding reference signal configuration, an MBSFN reference signal configuration, an uplink demodulation reference signal configuration, a reference signal hopping pattern, a PUSCH hopping pattern, a downlink control channel configuration, an uplink control channel configuration.

7. The method of claim 1 wherein the one or more parameters further comprise one or more of: the carrier frequency, a number of transmit antenna ports, a bandwidth, and a cyclic prefix length indication.

8. The method of claim 1 wherein the at least one physical layer characteristic comprises a reference signal configuration, the method further comprising: performing a measurement of a signal received over the second cell based on the reference signal configuration; and transmitting a measurement report.

9. The method of claim 2 wherein the cell identity is included in a request to add a secondary cell.

10. The method of claim 9 further comprising adding the second cell corresponding to the received cell identity.

11. The method of claim 1 wherein the first cell is configured on the same carrier frequency as the second cell.

12. The method of claim 1 wherein if the one or more parameters received at the user equipment does not include the carrier frequency, a number of transmit antenna ports, a bandwidth, or a cyclic prefix length indication, the UE assumes that the parameters not received have a same value in the second cell as in the first cell.

13. A method for signaling cell identity information in a wireless communications network, the method implemented by a network node serving a first cell configured on a first carrier frequency, the method comprising: transmitting, to a User Equipment (UE) over the first cell, one or more parameters associated with a second cell configured on a second carrier frequency; and wherein for each of the one or more parameters, the network node transmits the parameter only if the parameter has a different value in the second cell than in the first cell.

14. The method of claim 13 further comprising indicating to the UE to derive at least one physical layer characteristic for the second cell based on the one or more parameters.

15. The method of claim 13 wherein the one or more parameters comprise a cell identity of the second cell and a number of transmit antenna ports.

16. The method of claim 13 wherein the network node further serves the second cell, and wherein the method further comprises transmitting synchronization signals, reference signals or parts of system information over the second cell with reduced or zero power.

17. The method of claim 13 further comprising transmitting, over the first cell, an indication that no cell-specific reference signals are detectable in the second cell.

18. A mobile terminal comprising: communications interface circuitry configured to communicate information with one or more devices via a communications network; and processing circuitry operatively connected to the communications interface circuitry and configured to: receive, over the first cell, an indication that no cell-specific reference (CSR) signals are detectable in the second cell; and refrain from performing measurements on CSR signals in the second cell responsive to receiving the indication.

19. A network node comprising: a transceiver operatively connected to the configured to: transmit information to a User Equipment (UE) over a first cell configured on a first carrier frequency; and for each of one or more parameters associated with a second cell configured on a second carrier frequency, transmit the parameter to the UE only if the parameter has a different value in the second cell than in the first cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram illustrating the LTE downlink physical resource.

(2) FIG. 2 is a schematic diagram illustrating the LTE time-domain structure.

(3) FIG. 3 is a schematic diagram illustrating Carrier Aggregation.

(4) FIG. 4 is a schematic diagram illustrating inter-cell interference scenarios.

(5) FIG. 5 is a schematic diagram illustrating frequency separation between different layers in a heterogeneous network.

(6) FIG. 6 is a schematic diagram illustrating different deployment options for heterogeneous networks.

(7) FIG. 7 is a schematic diagram illustrating muting in a heterogeneous network.

(8) FIG. 8 is a schematic diagram illustrating inter-cell interference coordination (ICIC).

(9) FIG. 9 is a schematic diagram illustrating a wireless communications network according to an embodiment.

(10) FIG. 10 is a flow chart illustrating a method according to an embodiment.

(11) FIG. 11 is a flow chart illustrating a method according to an embodiment.

(12) FIG. 12 is a schematic diagram illustrating a wireless communications network according to an embodiment.

(13) FIG. 13 is a flow chart illustrating a method according to an embodiment.

(14) FIG. 14 is a flow chart illustrating a method according to an embodiment.

(15) FIG. 15 is a flow chart illustrating a method according to an embodiment.

(16) FIG. 16 is a flow chart illustrating a method according to an embodiment.

(17) FIG. 17 is a flow chart illustrating a method according to an embodiment.

(18) FIG. 18 is a block diagram illustrating a user equipment according to an embodiment.

(19) FIG. 19 is a block diagram illustrating a network node according to an embodiment.

ABBREVIATIONS

(20) CC Component Carrier

(21) CIF Carrier Indicator Field

(22) CRS Cell Specific Reference Signals

(23) CSG Closed Subscriber Group

(24) DCI Downlink Control Information

(25) HeNB Home eNB

(26) ICIC Inter-Cell Interference Coordination

(27) MBSFN Multi-Media Broadcast over a Single Frequency Network

(28) OFDM Orthogonal Frequency Division Multiple Access

(29) OSG Open Subscriber Group

(30) PBCH Physical Broadcast Channel

(31) PCC Primary Component Carrier

(32) PCFICH Physical Control Format Indicator Channel

(33) PDCCH Physical Downlink Control CHannel

(34) PDSCH Physical Downlink Shared Channel

(35) PHICH Physical Hybrid-ARQ Indicator Channel

(36) PSS Primary Synchronization Channel

(37) PUCCH Physical Uplink Control Channel

(38) PUSCH Physical Uplink Shared Channel

(39) RRC Radio Resource Control

(40) RS Reference Signals

(41) SRS Sounding Reference Signals

(42) SSS Secondary Synchronization Channel

(43) UL DMRS UL Demodulation Reference Signals

DETAILED DESCRIPTION

(44) As explained above, in certain scenarios it is necessary to reduce, or even set to zero, the transmission power of PSS/SSS and/or PBCH on one component carrier, in order to protect corresponding signals transmitted from another node. This is illustrated in FIG. 7, which shows how a macro cell protects PSS/SSS and PBCH from a pico cell by transmitting its corresponding signals with zero/reduced power on carrier f2. If a mobile terminal shall be able to connect to the macro cell even close to the pico cell, e.g. if the pico cell is a CSG cell to which the terminal does not have access, then the pico cell has to transmit PSS/SSS and PBCH with zero or reduced power on f1. This means that a mobile terminal may not be able to derive certain important parameters associated with the component carrier which is muted. For instance, the cell ID and number of TX antenna ports cannot be determined if the PSS/SSS and PBCH can't be detected. Without knowledge of the cell ID and/or the number of TX antenna ports corresponding to a given cell, or a given component carrier, the mobile terminal cannot determine reference signals, scrambling sequences, etc. for that component carrier, e.g. SCell. As already mentioned, the problem is not limited to scenarios where muting is applied, but may occur whenever the PSS/SSS and/or PBCH cannot be detected, for instance due to severe interference from a neighboring cell. In all these cases, the end result is that the mobile terminal will be unable to detect the presence of the cell, perform measurements, and/or establish communication with the cell.

(45) However, even if the mobile terminal is not able to detect the synchronization and broadcast channels, it may still be possible and beneficial for the terminal to establish communication with the cell. As mentioned earlier, synchronization and system information, such as PSS/SSS and PBCH, must be transmitted on certain well-defined resources. This is illustrated in FIG. 8, where a dotted square inside the data region schematically illustrates the location of synchronization channels. These channels are always transmitted in the same location in cells A and B, and if cell A and B use the same carrier frequency, interference will result. However, for data in the data region it is possible to use ICIC methods to ensure that transmissions do not collide between cells A and B. In this example, the frequency resources in the data region have been partitioned so that cell A uses one part of the data region, while cell B uses another part, as indicated by the slashed regions in FIG. 8. Thus, the data regions will not interfere with each other. Provided that a mobile terminal could detect and establish communications with both cells A and B, the mobile terminal should have no problem receiving and/or transmitting data that is comprised in the data region.

(46) In various embodiments of the present disclosure, the above-mentioned problem is addressed by transmitting at least one parameter associated with a cell, e.g. a secondary cell (SCell), in another cell, e.g. a primary cell (PCell). In other words, a parameter such as the cell ID of the cell, e.g. secondary serving cell (SCell) that is configured on the carrier frequency, e.g. component carrier which transmits PSS/SSS with reduced or zero power is signaled in another cell. Also, the number of transmit antenna ports a component carrier is configured with may be signaled in another cell if the PBCH cannot be detected, e.g. because it is transmitted with reduced/zero power. Furthermore, in some scenarios it may be possible to transmit CRS with reduced/zero power—in such cases it is possible to signal this to the terminal, to avoid unspecified behavior in the terminal.

(47) Thus, the mobile terminal receives the required parameters for a cell, e.g. SCell, which are not possible to detect and/or derive from the cell's own transmissions, from another cell, e.g. PCell, which the terminal is able to detect. With knowledge of cell ID and number of TX antenna ports, the mobile terminal is capable of reconstructing reference signals, scrambling sequences, etc. needed for uplink and downlink operation in the cell, e.g. SCell. Other parameters, such as carrier frequency, bandwidth and cyclic prefix length indication, may also be signaled in the other cell, e.g. PCell. However, in certain circumstances the mobile terminal may be able to assume default values for some or all parameters; thus, it may not be necessary to signal all these parameters in the other cell. As an example, a mobile terminal may assume that the number of antenna ports, bandwidth etc. are the same in the SCell as in the PCell, if these parameters are not signaled in the PCell.

(48) To perform mobility measurements, a mobile terminal needs to be able to reconstruct the cell-specific reference signals (CRS) and needs to know the carrier frequency of the other cell, e.g. SCell (secondary serving cell). Techniques for signaling the carrier frequency of a SCell to a mobile have previously been disclosed. For instance, see R2-103427, Change Request CR 0230 to 36.300, “Stage 2 description of Carrier Aggregation”, 3GPP TSG-RAN WG2 Meeting #70, Montreal, Canada, 10-14 May 2010. Given knowledge of the carrier frequency of the other cell, e.g. SCell, combined with the techniques disclosed herein for signaling the cell ID, a terminal can reconstruct the CRS and thus perform mobility measurements in the other cell, e.g. SCell.

(49) Some deployment scenarios may require that the CRS are transmitted with reduced/zero power in an SCell. In this case, demodulation by the mobile terminal relies on UE-specific reference signals. Even if a terminal is now capable to reconstruct the CRS it will not measure anything meaningful since no CRS are present. To avoid undesirable mobile terminal behavior, e.g., the mobile terminal is configured with a secondary cell SCell, but mobility measurements indicate that this cell is not present, it may be advantageous to signal to the terminal that no CRS are present, or at least they are not detectable, in the SCell. In such a case, the mobile terminal may be configured so that it does not provide any mobility measurements based on CRS on the corresponding cell object.

(50) Both the cell ID and number of transmit antenna ports are generally static parameters, and thus are expected to change only on a very slow basis. A good signaling choice is therefore to signal cell ID and the number of transmit antenna ports of a cell, e.g. SCell, using semi-statically signaling, e.g. RRC signaling, in another cell, e.g. the primary serving cell (PCell) or another SCell.

(51) This signaling is not needed in all scenarios, therefore signaling of these values may be enabled on an optional basis. This may be achieved e.g. by defining information elements for “Number of TX antenna ports of SCell” and “Cell ID of SCell” that are optionally included in a message of the semi-static signaling protocol. The required information may be transmitted to the terminal via dedicated signaling or via broadcast. Accordingly, a terminal configured with at least one secondary cell, SCell, receives required information regarding this secondary cell, SCell, via dedicated signaling or broadcasting. Thus, on top of previously defined system parameters a terminal may optionally receive additional parameters defined in this disclosure.

(52) Those skilled in the art will appreciate that cells configured on separate frequencies may sometimes use the same cell identity. In such cases, it may be unnecessary to explicitly signal this information to the mobile terminal, even if it is realized that a mobile terminal needs this information. Thus, according to one specific embodiment, if a terminal does not receive the newly defined information element “Cell ID of SCell”, then it reuses the cell ID from an already configured cell, either from the primary serving cell PCell or another configured secondary cell, e.g. from a second SCell that is used to convey system parameters for a first SCell. If a terminal, however, receives the information element “Cell ID of SCell” it will use this parameter to derive cell ID in the SCell.

(53) This same mechanism is also applicable to the new parameter “Number of TX antenna ports of SCell”. If a terminal does not receive this information element, it will apply the number of TX antenna ports in the primary serving cell PCell or another configured secondary cell, e.g., from a second SCell that is used to convey system parameters for the first SCell. If the information element “Number of TX antenna ports of SCell” is received by the terminal, on the other hand, it will assume this parameter to derive number of TX antenna ports in the SCell.

(54) If no CRS are transmitted, or if CRS are transmitted with reduced/zero power, in a secondary cell SCell this may lead to unspecified mobile terminal behavior. To avoid this, the optional information element “CRS not present in SCell” may be transmitted, in some embodiments. If this information element is received by the terminal it does not assume the presence of CRS in the secondary cell SCell. If this information element is not received the terminal assumes CRS are transmitted in the secondary cell SCell.

(55) A method in a user equipment according to an embodiment will now be described with reference to FIG. 9 and the flowchart in FIG. 10.

(56) FIG. 9 is a schematic drawing illustrating a wireless network 900 comprising a macro cell 910 and a pico cell, where the coverage area of the pico cell is contained within the coverage area of the macro cell 910. The macro cell 910 operates on carrier frequency f2, and is served by macro base station 940, e.g. an LTE eNB. The pico cell operates on carrier frequencies, or component carriers, f1 and f2, where f1 is a different carrier frequency from f2. Thus, there are actually two cells configured in the pico cell: a first cell 970 configured on component carrier f1, and a second cell 980 configured on component carrier f2. As described above, synchronization signals, reference signals, etc. will be transmitted in both cells 970 and 980. The pico cell, comprising cells 970 and 980, is served by pico base station 950, which may for instance be an LTE home base station, HeNB. A user equipment 920 is located within the coverage area of both the macro cell 910, and the cells 970 and 980. In this example, the user equipment 920 is a mobile terminal capable of carrier aggregation, e.g. an LTE Release 10-compliant UE. The user equipment 920 is initially connected to the first cell 970, which is configured on f1; thus, from the point of view of user equipment 920, the first cell 970 is the primary serving cell, or PCell. It would be advantageous for user equipment 920 to also add the second cell 980 as a secondary cell (SCell), since this would increase the available bandwidth for the user equipment 920. However, the assumption in this example is that user equipment 920 is not able to detect and/or decode control and synchronization information transmitted over the second cell 980, i.e. the cell configured on carrier frequency f2. As explained earlier, this problem may occur e.g. because the macro base station 940 is transmitting at a much higher power on f2, causing so much interference in the cell 980, and in particular on the synchronization channels PSS/SSS and broadcast channel PBCH, that the signal from the pico base station 950 on carrier f2 is not detectable. Therefore, user equipment 920 is not able to acquire necessary parameters, e.g. cell id, for the second cell 980, and it thus cannot add the second cell as an SCell using standard mechanisms.

(57) According to the method, the user equipment 920 receives, 1010, a request to add a secondary cell, SCell. The request is received over the first cell 970. The request to add the SCell comprises the cell identity of the second cell 980. In some variants, the cell identity is the physical cell identity of the second cell 980.

(58) In some variants of this embodiment, the request may also comprise other parameters associated with the second cell 980. For example, one or more of the parameters carrier frequency, number of transmit antenna ports, bandwidth, or cyclic prefix length indication related to the second cell 980 may be received over the first cell 970. However, if the user equipment 920 does not receive one or more of these parameters, the user equipment 920 may assume default values for any parameters that were not received. In particular, the user equipment 920 may assume that the non-received parameters have the same value in the second cell 980 as in the first cell 970. Therefore, it is not necessary that all parameters associated with the second cell 980 are received over the first cell 970.

(59) In some variants, the user equipment 920 also receives, 1020, an indication over the first cell 970 to use the received parameters, i.e. the cell id and any additional parameters, to derive at least one physical layer characteristic for the second cell 980. In other words, the indication tells the user equipment 920 that it should derive the physical layer characteristic from the received parameter, instead of trying to detect it in the air. An advantage of receiving the indication is that the user equipment does not need to spend time and resources on unnecessary attempts to decode signals from the second cell 980, which could not be successful anyway. However, in other variants the user equipment 920 always uses the received parameters, if present, to derive the physical layer characteristics. In yet other variants, the user equipment 920 first tries to detect the parameters for the second cell 980 over the air, and if this fails it uses the parameters received over the first cell 970.

(60) It should be noted that the indication may be received in the same message as the at least one parameter, or it may be received in a separate message. The indication may be realized as a flag, e.g. using one or more unused bits of an existing message. In another alternative, the mere presence of the at least one parameter may be regarded as the indication. Thus, the indication may be implicitly present in the message. The indication may be received on a broadcast channel in the first cell 970.

(61) After having received the cell id and possibly other parameters over the first cell 970, the user equipment derives, 1050, at least one physical layer characteristic for the second cell 980, based on the parameters. The physical layer characteristics may be e.g. scrambling codes, reference signal configurations, or control signaling configurations. In particular, the cell identity may be used to derive the cell-specific reference signal configuration, DMRS, SRS, or MBSFN reference signal configuration, reference signal hopping pattern, PUSCH hopping pattern, downlink control channel configuration, uplink control channel configuration, and scrambling codes for PUSCH, PDSCH, and for L1/L2 control signaling. It is pointed out that it is well known in the art how to derive these characteristics, once the required parameters are known. Thus, this procedure will not be described in further detail in this disclosure.

(62) Once the user equipment has derived at least one physical layer characteristic for the second cell 980, the user equipment 920 adds, 1060, a secondary cell corresponding to the received cell identity. That is to say, the user equipment 920 adds the second cell 980 as a secondary serving cell, or SCell. It is pointed out that once the necessary physical layer characteristics of the second cell 980 have been derived, the second cell 980 may be added as an SCell using known procedures, which will not be described further here.

(63) It is now possible for the user equipment 920 to use the additional resources provided by the SCell, i.e. the user equipment 920 may receive transmissions over component carrier f2, i.e. over the second cell 980. The user equipment 920 may additionally perform uplink transmissions on the uplink carrier which is linked to component carrier f2.

(64) In a variant of this embodiment, the user equipment 920 receives, 1030, over the first cell 970, an indication that no cell-specific reference signals are detectable in the second cell 980. The user equipment 920 may, in response to this indication, refrain from performing any measurement on cell-specific reference signals in the second cell, e.g. the user equipment 920 may refrain from mobility measurements based on CRS. This may be advantageous in cases where the CRS are muted, i.e. transmitted with reduced or zero power, in the second cell 980, as an attempt to measure on the undetectable CRS may result in unspecified behavior in the terminal. The same applies in deployments where CRS are transmitted, but high interference from neighboring cells makes it impossible to receive the CRS with sufficient good quality.

(65) In a further variant, the user equipment 920 receives, 1040, over the first cell 960, information indicating a user-specific reference signal configuration associated with the user equipment 920 in the second cell 980. This may be beneficial for instance when the cell-specific reference signals cannot be detected. As mentioned above, CRS are more prone to interference from other cells since they are typically transmitted on predefined resources. However, user-specific reference signals are transmitted in a pattern specific to the user equipment 920, so that they do not collide with reference signals transmitted in other cells. Therefore, it may be more advantageous for the user equipment 920 to perform measurements on user-specific reference signals, when these are available.

(66) Thus, according to this embodiment, the cell identity of the second cell 980 is transmitted over the first cell 970. The user equipment may use this cell id to derive various synchronization-related parameters associated with the second cell 980. This will enable the user equipment 920 to receive transmissions over the second cell 980.

(67) It should be noted that in FIG. 9, cell 980 has been indicated with a dashed circle, and drawn slightly smaller than cell 970 for ease of viewing. This does not necessarily reflect the relation between the actual geographical coverage areas of cells 970 and 980. As the skilled person will realize, cells 970 and 980 may have the same geographical coverage, or cell 970 may be smaller than cell 980, or their coverage areas may differ in various other ways due to e.g. different fading characteristics. Also, the actual coverage areas are not necessarily circular. It is further pointed out that, although the present embodiment is described in the context of the scenario of FIG. 9, the described method is applicable in other scenarios as well—for instance, in the scenario of FIG. 4(b), where the user equipment cannot hear a macro cell because of interference from a nearby CSG cell, or in a scenario where transmission on one carrier frequency is muted to protect signals in another cell, as described above. Thus, cells 970 and 980 may in other scenarios be served by a macro base station.

(68) Furthermore, cells 970 and 980 are not necessarily served by the same physical base station. The cells could, for instance, emanate from different remote radio heads, or they could even be served by two neighboring base stations, assuming that the coverage areas of cells 970 and 980 overlap, and that carrier aggregation across multiple base stations is supported.

(69) It should be noted that although the cell id and any additional parameters have been described here as being comprised in the request to add the secondary cell, it is equally possible to receive one or more of the parameters in a separate message. Also, one or more of the parameters may be received over a broadcast channel in the first cell 970, rather than in a dedicated message to the user equipment 920.

(70) A method in a network node according to an embodiment will now be described, with reference to FIG. 9 and the flowchart in FIG. 11.

(71) The scenario shown in FIG. 9 has already been described in connection with the previous embodiment. The present embodiment relates to a method performed in the network node 950, which serves the first cell 970 configured on carrier frequency f1, and the second cell 980 configured on carrier frequency f2. A user equipment 920 is connected to the first cell 970. As mentioned above, network node 950 may be realized as a pico or femto base station, e.g. as an LTE HeNB, but in some alternative scenarios the network node 950 may be a macro base station, such as an LTE eNB.

(72) In this embodiment, the network node 950 serves the second cell 980, and transmits, 1120, synchronization signals, reference signals or parts of system information over the second cell 980 with reduced or zero power. As explained above, a reason for this muting may be that there is another nearby cell which is also configured on carrier frequency f2, and which is heavily interfered by transmissions in cell 980. Thus, the network node 950 may mute certain signaling in order to protect another cell. However, this will also prevent user equipment 920 from detecting the cell 980.

(73) According to the method, the network node 950 transmits, 1110, a request to add a secondary cell, SCell. The request is transmitted over the first cell 970. The request to add the SCell comprises the cell identity of the second cell 980. In some variants, the cell identity is the physical cell identity of the second cell 980.

(74) In some variants of this embodiment, the request may also comprise one or more other parameters associated with the second cell 980, e.g. carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication.

(75) The network node 950 also transmits, 1110, an indication to use the at least one parameter to derive at least one physical layer characteristic for the second cell 980. In other words, the indication tells the user equipment 920 that it should derive the physical layer characteristic from the received parameter, instead of trying to detect it in the air. The indication may be transmitted in the same message as the at least one parameter, or in a separate message. The indication may be realized as a flag, e.g. using one or more unused bits of an existing message. Alternatively, the indication may be transmitted on a broadcast channel in the first cell 970.

(76) In some further variants, the network node 950 transmits a parameter only if it has a different value in the second cell 980 than in the first cell 970, or if it has a different value than a predetermined default value. For example, if the second cell 980 uses the same bandwidth and number of antenna ports as the first cell 970, those two parameters are not transmitted over the first cell 970. The user equipment 920 may then assume that the non-transmitted parameters have the same value as in the first cell, or that they have the same value as the predetermined default value.

(77) In a variant of this embodiment, the network node 950 transmits, 1130, over the first cell 970, an indication that no cell-specific reference signals are detectable in the second cell 980. The user equipment 920 may, in response to this indication, refrain from performing any measurement on cell-specific reference signals in the second cell, as described above.

(78) In some further variants, the network node 950 transmits, 1140, over the first cell, information indicating a user-specific reference signal configuration associated with the user equipment 920 in the second cell 980. The user-specific reference signal configuration may be used by the user equipment 920 as described in the previous embodiment.

(79) By transmitting the necessary parameters over the first cell 970, the network node 950 enables the user equipment 920 to derive physical layer characteristics that are required to add the second cell 980 as an SCell. Once the user equipment 920 has successfully added the SCell, network node 950 may transmit information to user equipment 920 over component carrier f2, i.e. over the second cell 980.

(80) As already stated in connection with the previous embodiment, the circles indicating cells 970 and 980 do not necessarily indicate the shape of the actual geographical coverage areas of the cells. It is further pointed out that in some scenarios, the network node 950 serves only the first cell 970, whereas the second cell 980 is served by another network node. This assumes that carrier aggregation across multiple nodes is supported, and that network node 950 acquires the required parameters associated with the second cell 980, e.g. from a message received from the network node which serves the second cell 980. It is also pointed out that, similarly to the previous embodiment, the present method is applicable even if muting is not applied in the second cell 980, since there could be various other reasons why user equipment 920 fails to detect the second cell 980.

(81) It should be noted that although the cell id and any additional parameters have been described here as being comprised in the request to add the secondary cell, it is equally possible to transmit one or more of the parameters in a separate message. Also, one or more of the parameters may be transmitted over a broadcast channel in the first cell 970, rather than in a dedicated message to the user equipment 920.

(82) A method in a user equipment according to another embodiment will now be described with reference to FIG. 12 and the flowchart in FIG. 13. This embodiment relates to mobility measurements performed by a user equipment 1210 in connected mode.

(83) FIG. 12 is a schematic drawing illustrating a wireless network 1200 comprising a first cell 1220 and a second cell 1230, with partly overlapping coverage areas. The first and second cells both operate on the same carrier frequency f1. The first cell 1220 is served by network node 1240, e.g. an LTE eNB. The second cell 1230 is served by network node 1250, e.g. another LTE eNB. Synchronization signals, reference signals, etc. will be transmitted in both cells 1220 and 1230. A user equipment 1210 is located within the coverage area of both cells 1220 and 1230, and is currently connected to cell 1220. The user equipment 1210 is moving in the direction of the arrow 1270. Thus, the user equipment 1210 is getting closer to network node 1250 and it would be advantageous for the user equipment 1210 to perform mobility measurements on cell 1230, so that a handover decision may eventually be made. However, in this example the user equipment 1210 is not able to detect and/or decode information transmitted over the second cell 1230. A possible cause of this problem is that network node 1240 is transmitting with a higher power on f1, causing severe interference to the synchronization channels, broadcast channels, and/or reference signals in cell 1230. Another possibility is that network node 1250 is transmitting with reduced or zero power on the synchronization and/or broadcast channels, for instance to protect nearby pico cell 1260 which is also configured to use carrier frequency f1. Therefore, user equipment 1210 is not able to derive necessary parameters, e.g. cell id, for the second cell 1230, which are needed to receive the cell-specific reference signals, CRS. Consequently, user equipment 1210 cannot perform mobility measurements on cell 1230, which may lead to reduced throughput for user equipment 1210 as it moves further away from network node 1240, and possibly even to a dropped connection if the user equipment 1210 moves into the region which is only covered by cell 1230, without being able to detect the presence of the cell.

(84) According to the method, the user equipment 1210 receives, 1310, a request to perform measurements on the second cell 1230. The request is received over the first cell 1220. The measurement request comprises the cell identity of the second cell 1230. In some variants, the cell identity is the physical cell identity of the second cell 1230.

(85) In some variants of this embodiment, the request may also comprise other parameters associated with the second cell 1230. For example, one or more of the parameters carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication related to the second cell 1230 may be received over the first cell 1220. The number of transmit antennas influence the CRS because each antenna port transmits its own cell-specific reference signals. To be able to reconstruct the CRS the user equipment 1210 needs to know if they are present or not; thus, it needs to know how many antenna ports are used for transmission. However, if the user equipment 1210 does not receive one or more of these parameters, the user equipment 1210 may assume default values for any parameters that were not received. In particular, the user equipment 1210 may assume that the non-received parameters have the same value in the second cell 1230 as in the first cell 1220. Therefore, it is not necessary that all parameters associated with the second cell 1230 are received over the first cell 1220.

(86) In some variants, the user equipment 1210 also receives, 1320, an indication over the first cell 1220 to use the received parameters, i.e. the cell id and any additional parameters, to derive at least one physical layer characteristic for the second cell 1230. In other words, the indication tells the user equipment 1210 that it should derive the physical layer characteristic from the received parameter, instead of trying to detect it in the air. An advantage of receiving the indication is that the user equipment does not need to spend time and resources on unnecessary attempt to decode signals from the second cell 1230, which could not be successful anyway. However, in other variants the user equipment 1210 always uses the received parameters, if present, to derive the physical layer characteristics. In yet other variants, the user equipment 1210 first tries to detect the parameters for the second cell 1230 over the air, and if this fails it uses the parameters received over the first cell 1220.

(87) It should be noted that the indication may be received in the same message as the at least one parameter, or it may be received in a separate message. The indication may be realized as a flag, e.g. using one or more unused bits of an existing message. In another alternative, the mere presence of the at least one parameter may be regarded as the indication. Thus, the indication may be implicitly present in the message. The indication may be received on a broadcast channel in the first cell 1220.

(88) After having received the cell id and possibly other parameters over the first cell 1220, the user equipment 1210 derives, 1330, the cell-specific reference signal configuration for the second cell 1230, based on the parameters. To be able to derive the CRS, the user equipment 1210 may need to derive other physical layer characteristics as well, e.g. the PBCH scrambling code.

(89) Once the CRS configuration has been determined, the user equipment 1210 performs a measurement of the CRS of the second cell 1230 using the derived CRS configuration. In other words, the user equipment 1210 performs a mobility measurement on cell 1230.

(90) The user equipment 1210 then transmits a measurement report comprising the result of the measurement to its serving network node, i.e. network node 1240 in this example. The serving network node may use the measurement report to make a handover decision, possibly handing over the connection with user equipment 1210 to cell 1230.

(91) In the present example, it has been assumed that user equipment 1210 receives the required parameters from its serving cell, i.e. cell 1220. However, it is also possible that the user equipment 1210 is not connected to the first cell 1220, but to a third cell (not shown in FIG. 12). If the parameters for the second cell 1230 are broadcast in the first cell 1220, the user equipment 1210 may be able to acquire the parameters even though it is not currently connected to the first cell 1220. Any measurement report would then be sent to the serving cell.

(92) It should be noted that although the cell id and any additional parameters have been described here as being comprised in the measurement request, it is equally possible to receive one or more of the parameters in a separate message. Also, one or more of the parameters may be received over a broadcast channel in the first cell 1220, rather than in a dedicated message to the user equipment 1210.

(93) A method in a user equipment according to another embodiment will now be described with reference to FIG. 12 and the flowchart in FIG. 14. The basic scenario of FIG. 12 has already been described above, i.e. user equipment 1210 is located in the mutual coverage areas of cells 1220 and 1230, and moving in the direction of arrow 1270 away from the coverage of cell 1220. However, in the present embodiment, user equipment 1210 is in idle mode, and it is desirable to perform mobility measurements on cell 1230 for the purpose of a possible cell reselection. As already explained above, this means that user equipment 1210 needs to measure on the cell-specific reference signals, CRS, of cell 1230; however, the user equipment 1210 cannot derive the CRS configuration because of interference from cell 1220.

(94) According to the method, the user equipment 1210 receives, 1410, at least one parameter associated with the second cell 1230. The request is received over the first cell 1220. The at least one parameter comprises the cell identity of the second cell 1230. In some variants, the cell identity is the physical cell identity of the second cell 1230.

(95) In some variants of this embodiment, the user equipment 1210 also receives other parameters associated with the second cell 1230. For example, one or more of the parameters carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication related to the second cell 1230 may be received over the first cell 1220. The number of transmit antennas influence the CRS, because each antenna port transmits its own cell-specific reference signals. To be able to reconstruct the CRS the user equipment 1210 needs to know if they are present or not; thus, it needs to know how many antenna ports are used for transmission. However, if the user equipment 1210 does not receive one or more of these parameters, the user equipment 1210 may assume default values for any parameters that were not received. In particular, the user equipment 1210 may assume that the non-received parameters have the same value in the second cell 1230 as in the first cell 1220. Therefore, it is not necessary that all parameters associated with the second cell 1230 are received over the first cell 1220.

(96) In some variants, the user equipment 1210 also receives, 1420, an indication over the first cell 1220 to use the received parameters, i.e. the cell id and any additional parameters, to derive at least one physical layer characteristic for the second cell 1230. In yet other variants, the user equipment 1210 first tries to detect the parameters for the second cell 1230 over the air, and if this fails it uses the parameters received over the first cell 1220. It should be noted that the indication may be received in the same message as the at least one parameter, or it may be received in a separate message. The indication may be realized as a flag, e.g. using one or more unused bits of an existing message. In another alternative, the mere presence of the at least one parameter may be regarded as the indication. Thus, the indication may be implicitly present in the message.

(97) Note that in this embodiment, the one or more parameters, and the indication, are all received on a broadcast channel in the first cell 1220, since the user equipment 1210 is in idle mode.

(98) After having received the cell id and possibly other parameters over the first cell 1220, the user equipment 1210 derives, 1430, the cell-specific reference signal configuration for the second cell 1230, based on the parameters. To be able to derive the CRS, the user equipment 1210 may need to derive other physical layer characteristics as well, e.g. the PBCH scrambling code.

(99) Once the CRS configuration has been determined, the user equipment 1210 performs a measurement, 1440, on the CRS of the second cell 1230 using the derived CRS configuration. In other words, the user equipment 1210 performs a mobility measurement on cell 1230.

(100) Depending on the result of the measurement, the user equipment 1210 may decide to initiate a cell reselection procedure, according to known mechanisms.

(101) A method in a network node according to another embodiment will now be described with reference to FIG. 12 and the flowchart in FIG. 15. Here, a scenario is described where network node 1240 requests user equipment 1210 to perform mobility measurements on cell 1230; thus, the embodiment is similar to the one described in connection with FIG. 13 above, but here the focus is on a method performed in the network node 1240.

(102) According to the method, the network node 1240 transmits, 1510, a request to the user equipment 1210 to perform measurements on the second cell 1230. The request is transmitted over the first cell 1220. The measurement request comprises the cell identity of the second cell 1230. In some variants, the cell identity is the physical cell identity of the second cell 1230.

(103) In some variants of this embodiment, the request may also comprise other parameters associated with the second cell 1230. For example, one or more of the parameters carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication related to the second cell 1230 may be transmitted over the first cell 1220. The number of transmit antennas influence the CRS because each antenna port transmits its own cell-specific reference signals. To be able to reconstruct the CRS the user equipment 1210 needs to know if they are present or not; thus, it needs to know how many antenna ports are used for transmission.

(104) The network node 1240 also transmits, 1510, an indication to use the at least one parameter to derive at least one physical layer characteristic for the second cell 1230. In other words, the indication tells the user equipment 1210 that it should derive the physical layer characteristic from the received parameter, instead of trying to detect it in the air. The indication may be transmitted in the same message as the at least one parameter, or in a separate message. The indication may be realized as a flag, e.g. using one or more unused bits of an existing message. Alternatively, the indication may be transmitted on a broadcast channel in the first cell 1220. In another alternative, the mere presence of the at least one parameter may be regarded as the indication. Thus, the indication may be implicitly present in the message.

(105) By transmitting the parameters and indication over the first cell 1220, the network node 1240 enables the user equipment 1210 to derive the necessary physical layer characteristics for the second cell 1230. This will allow the user equipment 1210 to perform the requested measurements even it could not initially detect cell 1230.

(106) The network node 1240 then receives, 1530, a measurement report from user equipment 1210. Network node 1240 may use the measurement report to make a handover decision, possibly handing over the connection with user equipment 1210 to cell 1230.

(107) In some variants of this embodiment, the network node 1240 serves the second cell 1230, and transmits, 1520, synchronization signals, reference signals or parts of system information over the second cell 1230 with reduced or zero power. As explained above, a reason for this muting may be that there is another nearby cell which is also configured on carrier frequency f1, and which is heavily interfered by transmissions in cell 1230. Thus, the network node 1240 may mute certain signaling in order to protect pico cell 1260. However, this may also prevent user equipment 1210 from detecting the cell 1230. It should be noted, however, that the method is also applicable when muting is not used, since there are various other reasons that could prevent user equipment 1210 from detecting signals in cell 1230.

(108) It should be noted that although the cell id and any additional parameters have been described here as being comprised in the measurement request, it is equally possible to transmit one or more of the parameters in a separate message. Also, one or more of the parameters may be transmitted over a broadcast channel in the first cell 1220, rather than in a dedicated message to the user equipment 1210.

(109) A general method performed in a user equipment according to several embodiments will now be described with reference to the flow chart of FIG. 16.

(110) The user equipment receives, 1610, over a first cell configured on a carrier frequency, at least one parameter associated with a second cell configured on a carrier frequency. The at least one parameter comprises a cell identity.

(111) As mentioned in the specific embodiments discussed above, the first and second cells may be configured on the same, or different, carrier frequencies. In some embodiments, the first cell is the PCell of the user equipment.

(112) In some embodiments, the user equipment also receives, 1620, over the first cell, an indication to use the at least one parameter to derive at least one physical characteristic for the second cell.

(113) In some embodiments, the user equipment also receives, 1630, over the first cell, an indication that no CRS are detectable in the second cell.

(114) In some further embodiments, the user equipment receives, 1640, an indication of a user-specific reference signal configuration over the first cell.

(115) The user equipment then derives, 1650, at least one physical layer characteristic for the second cell based on the received at least one parameter, thereby enabling the user equipment to receive transmissions over the second cell. In some embodiments, the user equipment may proceed to add the second cell as an SCell. In other embodiments, the user equipment may derive a CRS configuration for the second cell, and use this to perform mobility measurements in idle mode or connected mode.

(116) A general method performed in a network node according to several embodiments will now be described with reference to the flow chart of FIG. 17. The network node serves a first cell configured on a carrier frequency.

(117) According to the method, the network node transmits, 1710, over the first cell, at least one parameter associated with a second cell configured on a carrier frequency. The at least one parameter comprises a cell identity. The network node also transmits an indication to use the at least one parameter to derive at least one physical layer characteristic for the second cell. The cell identity and possible other parameters may be comprised in a measurement request message sent to a user equipment, or they may be included in a request to add the second cell as an SCell.

(118) In some embodiments, the network node serves also the second cell, and transmits synchronization signals, reference signals, or part of system information over the second cell with reduced or zero power.

(119) In some embodiments, the network node also transmits, 1730, over the first cell, an indication that no CRS are detectable in the second cell.

(120) In some further embodiments, the network node transmits, 1740, an indication of a user-specific reference signal configuration over the first cell.

(121) FIGS. 18 and 19 illustrate example implementations of user equipment 920, 1110, and network node 940, 1140. It is pointed out that these devices may include computer-based circuitry, such as one or more circuits based on microprocessors, digital signal processors, ASICs, FPGAs, or other programmable or programmed digital processing circuitry. The operation of these devices may be implemented in whole or in part by configuring the device via the execution of stored computer programs, held in memory or other computer-readable media to which the device has access. Thus, it should be appreciated that the processing circuits illustrated in FIGS. 18 and 19 may be implemented in hardware, software, or a combination of both.

(122) FIG. 18 illustrates a user equipment 1800, comprising a transceiver 1810 and one or more processing circuits 1820. The processing circuits 1820 are configured to receive, over a first cell 970 configured on a carrier frequency, at least one parameter associated with a second cell 980 configured on a carrier frequency. The at least one parameter comprises a cell identity. The processing circuits 1820 are further configured to derive at least one physical layer characteristic for the second cell 980 based on the received at least one parameter, thereby enabling the user equipment 920 to receive transmissions over the second cell 980. The at least one parameter may further comprise one or more of: carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication.

(123) In some variants, the processing circuits 1820 are further configured to receive, over the first cell 970, an indication that the user equipment 920 should use the received at least one parameter to derive at least one physical layer characteristic for the second cell 980. The at least one physical layer characteristic may comprise one or more of: a PUSCH, PDSCH, L1/L2 control signaling or CRC of PBCH scrambling code, a cell-specific reference signal configuration, a sounding reference signal configuration, an MBSFN reference signal configuration, an uplink demodulation reference signal configuration, a downlink or uplink control signaling configuration, a reference signal hopping pattern, or a PUSCH hopping pattern.

(124) In some further variants, the processing circuits 1820 are further configured to receive, over the first cell 970, an indication that no cell-specific reference signals are detectable in the second cell 980. The processing circuits 1820 may be further configured to, in response to the indication that no cell-specific reference signals are detectable, not attempt to perform any measurement on cell-specific reference signals in the second cell 980.

(125) In some variants, the processing circuits 1820 are further configured to receive, over the first cell 970, information indicating a user-specific reference signal configuration associated with the user equipment 920 in the second cell 980.

(126) In some variants, the processing circuits 1820 are further configured to receive the at least one parameter over a broadcast channel.

(127) In some other variants, the processing circuits 1820 are configured to receive the at least one parameter in a measurement request. The processing circuits 1820 may be further configured to detect the second cell (980) by means of the cell identity received in the measurement request message. The processing circuits 1820 may be further configured to perform a measurement of a signal, e.g. a cell-specific reference signal, received over the second cell 980, by means of a received reference signal configuration, and to transmit a measurement report.

(128) In some other variants, the processing circuits 1820 are configured to receive the at least one parameter in a request to add a secondary cell. The processing circuits 1820 may be further configured to add a secondary cell corresponding to the received cell identity.

(129) In some variants, the processing circuits 1820 are configured to assume that, if the user equipment 920 does not receive one or more of the parameters carrier frequency, number of transmit antenna ports, bandwidth, or cyclic prefix length indication, the parameters not received have the same value in the second cell 980 as in the first cell 970.

(130) The user equipment 1800 may comprise more than one transceiver.

(131) FIG. 19 illustrates a network node 1900, comprising a transceiver 1910 and one or more processing circuits 1920. The processing circuits 1920 are configured to transmit, over a first cell 970 configured on a carrier frequency, at least one parameter associated with a second cell 980 configured on a carrier frequency, wherein the at least one parameter comprises a cell identity. The processing circuits 1920 are further configured to transmit an indication to use the at least one parameter to derive at least one physical layer characteristic for the second cell 980. The at least one parameter may further comprise one or more of: carrier frequency, number of transmit antenna ports, bandwidth, cyclic prefix length indication.

(132) In some variants, the processing circuits 1920 are further configured to transmit synchronization signals, reference signals or parts of system information over the second cell 980 with reduced or zero power;

(133) In some variants, the processing circuits 1920 are further configured to transmit, over the first cell 970, an indication that no cell-specific reference signals are detectable in the second cell 980.

(134) In some variants, the processing circuits 1920 are further configured to transmit, over the first cell 970, information indicating a user-specific reference signal configuration associated with a user equipment 920 in the second cell 980.

(135) In some variants, the processing circuits 1920 are further configured to perform the transmissions over a broadcast channel.

(136) In some other variants, the processing circuits 1920 are further configured to perform the transmissions in a dedicated message to a user equipment 920, e.g. a measurement request or a request to add a secondary cell.

(137) In some variants, the processing circuits 1920 are further configured to transmit a parameter only if it has a different value in the second cell 980 than in the first cell 970.

(138) The network node 1900 may comprise more than one transceiver.

(139) The solutions described above have been detailed in connection with carrier aggregation and heterogeneous networks, as specified for LTE networks. However, those skilled in the art will appreciate that the techniques and concepts described herein are more generally applicable to other wireless communication systems, where interference prevents a mobile terminal from detecting and/or communicating with a cell. Particular embodiments disclosed herein address carrier aggregation and/or the layered use of primary and secondary cells, i.e. heterogeneous systems in general. Thus, the present disclosure is not limited to LTE implementations.

(140) Some embodiments disclosed herein enable acquisition of cell ID of a cell configured on a component carrier and, optionally, number of transmit antenna ports, carrier frequency, bandwidth, cyclic prefix length indication for a component carrier on which PSS/SSS and PBCH are transmitted with reduced/zero power or received with bad quality due to high interference. This is needed in carrier aggregation based heterogeneous network deployments.

(141) Those skilled in the art will further appreciate that the various methods and processes described herein may be implemented using various hardware configurations, generally, but not necessarily including the use of one or more microprocessors, microcontrollers, digital signal processors, or the like, coupled to memory storing software instructions for carrying out the techniques described herein. As the design and cost tradeoffs for the various hardware approaches, which may depend on system-level requirements that are outside the scope of the present disclosure, are well known to those of ordinary skill in the art, further details of specific hardware implementations are not provided herein.

(142) Various embodiments of the techniques and concepts include radio base stations, such as LTE eNBs, comprising processing circuits configured to carry out the processes discussed above. Other embodiments include mobile terminals comprising processing circuits configured to carry out processes complementary to those performed by the base stations, plus, in some cases, additional processes.

(143) Thus, the present disclosure is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the disclosure, which is defined by the appending claims.

(144) When the word “comprise” or “comprising” is used in this disclosure, it is intended to be interpreted as non-limiting, i.e. meaning “consist at least of”.