Abstract:
There is provided a method of implementing carrier aggregation on a first transceiver. The method comprises receiving and decoding, during a first subframe, channel quality information from user equipment and transferring, before the expiry of a second subframe immediately following the first subframe, the decoded channel quality information over a direct physical link to a second transceiver, for use in decoding further channel quality information from the user equipment.

Description:
[0001]    The invention relates to a method of implementing carrier aggregation, a transceiver, a test setup, and a method of examining the performance of user equipment operating according to one or more predefined standards, for example the 3GPP standard. 
       BACKGROUND 
       [0002]    Test setups running protocol compliance toolsets may be used to examine the performance of user equipment operating according to one or more predefined standards, for example to test and certify that user equipment conforms to the relevant standard(s). The toolsets may be used to define scripts representing configuration scenarios and to run interoperability tests and development tests to examine conformance. For example, a system for emulating LTE-Advanced Carrier Aggregation can be provided, in which the Component Carriers (base stations or cells) being aggregated reside on multiple hardware units or transceivers. 
         [0003]    LTE-Advanced Carrier Aggregation is a 3GPP Release 10 feature introduced to increase the data rates which can he achieved by a connected device such as an LTE-Advanced capable mobile (UE). With Carrier Aggregation, UE is simultaneously connected to multiple cells (referred as Component Carriers in 3GPP terminology). A maximum of 5 such Component Carriers can be aggregated. Both intra- and inter-band Carrier Aggregation is envisaged i.e. the cells being aggregated can be on different RF frequencies. Some emulation scenarios for Carrier Aggregation are implemented by interconnecting multiple transceiver units implementing the physical layer of the aggregated Component Carriers. These multiple transceiver units are controlled by a common MAC scheduler via an interconnect mechanism such as an Ethernet switch. 
         [0004]    When in a connected state with the network, UE can be configured to periodically send channel status information about the quality of the channel as affected by propagation conditions and interfering sources. Such channel status information is of different types: 
         [0005]    a) Rank Indicator/Precoding Type Indicator (RI/PTI) bits, which indicate the optimum number of independent downlink data streams which can be received at the UE; 
         [0006]    b) Channel Quality Indicator/Precoding Matrix Indicator (CQI/PMI) bits, which provide a measure of the interference conditions and preferred ratios of information bits versus channel capacity (channel coding rate). 
         [0007]    Some emulation scenarios require implementation of configurations where values of periodic CQI/PMI are conditioned by the last reported values of RI/PTI. Hence, the most recently reported value of RI/PTI is necessary to ensure successful decoding of subsequent subframes with CQI/PMI transmissions. 
       SUMMARY 
       [0008]    The inventor has made the discovery through analysis and creation of a large number of unique configuration scenarios that some scenarios require implementation of configurations in which periodic RI/PTI and CQI/PMI are reported by the UE in consecutive subframes, on separate Component Carriers, which may be implemented on separate transceiver units. The term “subframe” in LTE and LTE-Advanced terminology refers to a time unit of one millisecond and is a basic unit of downlink/uplink transmissions to/from the UE. However, it is to be understood that the term subframe as used in the claims is not so limited and may refer to other time periods. 
         [0009]    In the scenarios described above, it would be necessary to transfer the decoded RI/PTI from the transceiver receiving the RI/PTI to the transceiver expected to receive the subframe with CQI/PMI as quickly as possible. If excessive latency/delay occurs, for example due to communication with the common MAC scheduler, then the transceiver expected to receive the subframe with CQI/PMI will be unable to successfully decode the CQI/PMI and/or data bits received in that subframe. This will trigger connection failures to the UE. 
         [0010]    Owing to his discovery, the inventor is able to address the non-obvious problem of reducing latency for RI/PTI transfer, a problem which is not known or obvious from the available prior art and which is addressed by the invention described in this document. Inc invention may provide a dedicated Serial Peripheral Interface (SPI) link for interconnecting the transceivers, for example in a daisy-chain fashion. A firmware-defined RI/PTI controller module implemented on each transceiver may be provided to control configuration of RI/PTI for uplink transmissions expected from the UE without the need to involve a common scheduler coil entity, which conventional wisdom dictates as being necessary in such arrangements. 
         [0011]    According to a first aspect, there is provided a method of implementing carrier aggregation on a first transceiver, the method comprising: 
         [0012]    receiving and decoding, during a first subframe, channel quality information from user equipment and transferring, before the expiry of a second subframe immediately following the first subframe, the decoded channel quality information over a direct physical link to a second transceiver, for use in decoding further channel quality information from the user equipment. 
         [0013]    The direct physical link may comprise a serial peripheral interface link, and the method may comprise controlling the serial peripheral interface link to perform the transfer of decoded channel quality information. 
         [0014]    According to a second aspect, there is provided a first transceiver configured to carry out the method of the first aspect. 
         [0015]    According to a third aspect, there is provided a test setup configured to examine the performance of user equipment operating according to one or more predefined standards, the test setup comprising: 
         [0016]    the first transceiver of the second aspect, configured to emulate a base station and to communicate with the user equipment under test according to a predefined test script representing a configuration scenario. 
         [0017]    The test setup may be configured to run one or more of a conformance toolset, an interoperability testing toolset, a development toolset, and a protocol compliance toolset, where those toolsets are implemented in software. Additionally or alternatively, the toolsets may be implemented in hardware, or in any one or more of hardware, software and firmware. 
         [0018]    Examining the performance of user equipment operating according to one or more predefined standards may comprise examining the conformance of the user equipment with those standards, for example. In other examples, examining performance may comprise examining for interoperability or for development purposes. 
         [0019]    The test setup may comprise the second transceiver connected to the first transceiver by the direct link, at least one further transceiver and at least one further direct link, wherein the direct links interconnect the transceivers in a daisy chain. 
         [0020]    According to a fourth aspect, there is provided a computer-readable medium comprising stored thereon instructions which, when executed by a computer, cause the computer to carry out the method of the first aspect. The instructions may be implemented for example in software, firmware, or both. In one example, there may be provided a software module comprising a controller module which provides configuration information to a firmware module which performs decode operations (for example decoding of RI/PTI and CQI/PMI). 
         [0021]    According to a fifth aspect, there is provided a method of examining the performance of user equipment operating according to one or more predefined standards, the method comprising: 
         [0022]    emulating a base station using a first transceiver configured to communicate with user equipment under test according to a predefined test script representing a configuration scenario; and 
         [0023]    performing the method of the first aspect. 
         [0024]    The claimed subject-matter may facilitate the design and implementation of radio transceivers which support LTE-Advanced Carrier Aggregation without restrictions on uplink scheduling configurations. 
         [0025]    The present invention includes one or more aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. 
         [0026]    The above summary is intended to be merely exemplary and non-limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    A description will now be given, by way of example only, with reference to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a diagram illustrating a test setup running a protocol compliance toolset being used to examine conformance of user equipment with predefined standards; 
           [0029]      FIG. 2  is a flowchart representing part of a method of implementing carrier aggregation. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  shows a test setup  100  running a protocol compliance toolset being used to examine conformance of user equipment  114  with predefined standards. 
         [0031]    The test setup  100  comprises a control PC  102  for effecting overall control of the system, an Ethernet switch  100  managed by a controller/scheduler  104  for handling communications between the transceivers, and three transceivers being a first transceiver  108 , a second transceiver  110  and a third transceiver  112 . Although  FIG. 1  shows three transceivers, it is to be understood that any number of transceivers can be interconnected depending on the carrier aggregation scenario, with for example anywhere between 2-5 transceivers being interconnected. 
         [0032]    User equipment  114  under test is also shown, and communicates with the first transceiver  108  using a first RF link with the second transceiver  110  using a second RF link RF#2, and with the third transceiver  112  using a third RF link RF#3. The first transceiver  108  emulates a first component carrier, the second transceiver  110  emulates a second component carrier, and the third transceiver  112  emulates a third component carrier. 
         [0033]    As part of LTE-Advanced Carrier Aggregation the user equipment  114  may be simultaneously connected to multiple component carriers to increase data rates, and the protocol compliance toolset implements emulation scenarios for Carrier Aggregation, with the interconnected multiple transceivers  108 ,  110 ,  112  implementing the physical layer of the aggregated Component Carriers under the control of the controller/scheduler  104  via the Ethernet switch  106 . 
         [0034]    The control and configuration of the physical layer as implemented on the multiple transceivers  108 ,  110 ,  112 , along with the scheduling of user data, are performed by the controller/scheduler  104 . 
         [0035]    When in a connected state with the network, the user equipment  114  can be configured to periodically send channel status information about the quality of the channel as affected by propagation conditions and interfering sources. Such channel status information may include. 
         [0036]    a) Rank Indicator/Precoding Type Indicator (RI/PTI) hits, which indicate the optimum number of independent downlink data streams which can be received at the UE; 
         [0037]    b) Channel Quality Indicator/Precoding Matrix Indicator (CQI/PMI) bits, which provide a measure of the interference conditions and preferred ratios of information bits versus channel capacity (channel coding rate). 
         [0038]    Depending on scheduler operation, uplink transmissions from the user equipment  114  can be scheduled on component carriers emulated on separate transceivers  108 ,  110 ,  112  in consecutive subframes. Under specific configuration conditions, decoded RI/PTI bits received from the user equipment  114  in a particular subframe can be necessary for decoding CQI/PMI bits in the very next subframe. 
         [0039]    In order to reduce the latency of sharing the RI/PTI values across the multiple transceivers  108 ,  110 ,  112 , each of the transceivers  108 ,  110 ,  112  is provisioned with a dedicated, direct physical link, in the form of a Serial Peripheral interface (SPI) link  116 , for interconnecting the transceivers  108 ,  110 ,  112  in a daisy-chain fashion. RI/PTI values decoded on each transceiver  108 ,  110 ,  112  are shared amongst the multiple transceivers participating in Carrier Aggregation using the SPI link  116 , for example by being broadcast to all transceivers  108 ,  110 ,  112  along the daisy chair. Three such SPI links  116  interconnecting the three transceivers  108 ,  110 ,  112  are shown in  FIG. 1 . 
         [0040]      FIG. 2  shows part of a method of implementing carrier aggregation. The method includes decoding RI/PTI bits ( 202 ), before determining ( 204 ) whether or rot to transmit ( 206 ) the decoded RI/PTI bits to a further transceiver over the SPI link  116 . The determination ( 204 ) may depend on higher layer configuration as defined by test script/configuration whether the transceiver is part of a carrier aggregation set. This information is available to the controller/scheduler  104  as part of configuration information. The received, decoded RI/PTI bits may be used in an update by the receiving transceiver ( 208 ), before being used to decode CQI values ( 210 ). The controller/scheduler  104  may provide configuration information determining whether the update ( 208 ) needs to be executed on a particular transceiver for a particular subframe. In a parallel pathway, the decoded RI/PTI bits are used in an update at the decoding transceiver ( 212 ), since, depending on the test configuration, the CGI/PMI can be received on the same transceiver as that on which the RI/PTI was received. 
         [0041]    It will be appreciated that the aforementioned circuitry may have other functions in addition to the mentioned functions, and that these functions may be performed by the same circuit. 
         [0042]    The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the an that various modifications may be made within the scope of the invention.