GB2494394A

GB2494394A - Spatial hashing for enhanced control channel search spaces

Info

Publication number: GB2494394A
Application number: GB1115197.4A
Authority: GB
Inventors: Tommi T Koivisto; Timo E Roman; Mihai Enescu
Original assignee: Renesas Mobile Corp
Current assignee: Renesas Electronics Corp
Priority date: 2011-09-02
Filing date: 2011-09-02
Publication date: 2013-03-13
Anticipated expiration: 2031-09-02
Also published as: GB2494394B; GB201115197D0

Abstract

The present invention provides a method, apparatus and a computer program product for spatial hashing for enhanced control channel search spaces. The present invention includes defining a control channel search space for searching for control channel candidates, defining search space locations within the search space, grouping the search space locations into a plurality of subsets of search space locations, associating each subset of search space locations with an antenna port and for each of a plurality of subframes, changing the search space locations from a first subset of search space locations to a second subset of search space locations.

Description

I

Improvements Relating to Enhanced Control Channel Search Spaces

Technical Field

The present application relates generally to an apparatus and method and a computer program product for spatial hashing for enhanced control channel search spaces.

Background

The following meanings for the abbreviations used in this specification apply: 3GPP The Generation Partnership Project BS Base Station CCE Control Channel Element CRS Common Reference Symbols DCI Downlink Control Information DM-RS Demodulation Reference Symbols eNB evolved NodeB FSTD Frequency-Switched Transmit Diversity LTE Long Term Evolution MIMO Multiple Input Multiple Output MIJ-MIMO Multi-user MIMO PDCCH Physical Downlink Control Channel ePDCCH cnhanccd Physical Downlink Control Channel PH 1CM Physical HARQ Indicator Channel QPSK Quadrature Phase Shift Keying RE Resource Element RS Reference Signal SFBC Space-Frequency Block Coding TIE User Equipment

I

Work on Release 10 of the 3th Generation Partnership Project (3GPP) Long Term Evolution (LTE) specification work is in its final stages. It includes several new features related to downlink and uplink MIMO, relays, bandwidth extension via carrier aggregation and enhanced inter-cell interference coordination (cICIC).

In the meantime, 3GPP has also started working on the next release of the LTE specifications, i.e. Release 11. One ongoing Study Item relates to doilink MIMO enhancements, one topic of which is downlink control signaling enhancements. Current downlink control signaling is based on common reference signals which are not precoded and are broadcast all over the cell. When multiple antennas are in use at an evolved NodeB (eNodeB), transmit diversity is applied, for example, space-frequency block coding (SFBC) in case of 2 Tx and space-frequency block coding frequency-switched transmit diversity (SFBC-FSTD) in case of 4 Tx. The mapping of the control channels to resource elements (REs) is fixed and based on cell ID. The current Study Item aims at enhancing downlink control channels, 111cc the physical downlink control channel (PDCCH) or the physical hybrid-ARQ indicator channel (PHICH) in terms of capacity (spectral efficiency) by means of more advanced multi-antenna techniques, e.g. closed-loop single-user multiple input multiple output (SU-MTMO) or multi-user (MU-) MIMO or even Coordinated multi-point (CoMP) transmission. At the same time another goal is to allow more flexibility in the mapping to resource elements in order to improve inter-cell interference coordination possibilities for control channels.

The enhanced PDCCH (cPDCCI-1) is assumed in the description hereafter to be based on UE-specific TJE-RS) reference signals (RS), which can be seen as ePDCCH specific RS in case each cPDCCH is transmitted using rank 1 transmission. These liE-specific RS can be in the form of currently existing Demodulation-RS (DM-RS), which have been specified during Release 9 and Release 10 or one may also envision a new type of UE-specific RS dedicated to cPDCCH demodulation with its own orthogonal port multiplexing scheme, RE mapping, sequence generation, etc. Release 9/10 DM-RS have an overhead of 12 REs for ranks I and 2 and 24 REs for ranks 3-8. Separate precodcd UE-spccitic reference signals arc transmitted on each spatial layer, and liE demodulation is based on these reference signals as they allow the TIE to estimate the precoded transmission channel.

There needs to be some flexibility in the resource mapping for cPDCCH since ePDCCHs will be transmitted to multiple liEs in the same subframe (i.e. to provide multiple access capability). On the other hand, the UE has no prior knowledge of the resource mapping before starting to decode ePDCCH. At the same time, the ePDCCH may be link-adapted so the UE does not know the coding rate either. In Release 8 the used modulation is QPSK; however, the modulation could become one additional unknown variable for cPDCCH as higher-order modulations may be considered in order to improve the spectral efficiency.

Finally, the used downlink control information (DCI) format is obviously unknown to the UE prior to decoding -in particular the length of the DCI format that is needed for channel decoding.

With the enhanced PDCCI-1, when multiple spatial layers are utilized, the UE will not know which spatial layer is assigned to, i.e. which UE-specific RS port is/are associated to, its ePDCCH transmission. So, again one more unknown variable is brought into the decoding process.

Hence overall there are many unknown variables which the liE would need to know or hypothesize over for proper ePDCCH decoding.

In Release 8, the concept of blind decoding is utilized to overcome the above-mentioned issues. It means that the liE performs several blind attempts to decode PDCCH with different assumptions about the coding rate, resource mapping and length of the DCI format. When the cyclic redundancy check (CRC) is successful, the UE can assume that it has successfully decoded PDCCH and that the corresponding hypotheses on the coding rate (i.e. number of CCE5), resource mapping and length of the DCI format (i.e. DCI format payload size) are then valid.

Such blind decoding needs to be limited in order to avoid excessive UE decoding complexity and latency in decoding control information. Therefore, the concepts of control channel elements (CCEs), CCE aggregation tree and PDCCH search space have been introduced. The resource element space for PDCCI-ls has been divided into CCEs which in Release 8 consist of 36 resource elements each. PDCCH REs are first dc-mapped at the UE in the form of a list of consecutive CCEs. The UE attempts to decode a number of DCI formats of pre-defined sizes from either 1, 2, 4 or 8 aggregated CCEs. In other words when attempting to decode, the liE assumes that each DCI format of pre-defined size is mapped to 1,2,4,8)x36 resource elcments, essentially implying the used coding rate.

This number of CCEs { 1,2,4,8) is called aggregation level. For each aggregation level, there are multiple locations from which the UE searches for the DCI format within the list of received CCEs. The set of all locations that the TIE will need to search through is called the PDCCH search space. The search space is divided into a common search space (typically used for system information scheduling) and a UE-specific search space (typically used for scheduling PDSCH or for UL grants).

Figure 1 shows an illustration of the Release 8 PDCCH CCE aggregation tree and the hashing function changing the search space from subframe to subframe.

The structure of Rel-.8 PDCCH is illustrated in the example of Figure 1 where the full PDCCH resource space consists of altogether 16 CCEs. With 16 CCEs, at aggregation levels { 1,2,4,8) there are 16,8,4,2} possible search space locations altogether respectively, organized in a tree structure as illustrated in the figure. The search space of a single UE cannot span the full CCE space as this would mean a prohibitively high number of blind decoding attempts for the UE.

Hence, the PDCCH search space for a given UE consists only of certain pre-defined starting locations at each aggregation level -in this example there are {3,3, 1,1} locations on aggregation levels {1,2,4,8} respectively, i.e. the full search space size is then 8 locations from which the liE needs to search for the PDCCI-l.

From eNB perspective, the search space concept means that the eNB can only schedule PDCCH for the TIE in these search space locations. In other words, the PDCCH scheduling is restricted. Hence, it is possible that there would be free resources in the overall PDCCH resource space but the UE cannot be scheduled since there are no free resources within the TIE search space (for example, some other UE#2 has been scheduled to the PDCCH resources overlapping either partially or totally to the UE#l search space). Such an event is called blocking, and there is a desire to minimize the probability of blocking events. liEs scheduled on high aggregation levels present particular problems when it comes to blocking. For example in the ease of Figure 1, another TIE scheduled on aggregation level 8 on CCEs 0-7 in subframe n would block aggregation levels 1,2 and 4 completely for the liE in the example.

In order to alleviate the blocking issue, the concept of hashing function was introduced in Release 8 for PDCCH. Essentially the hashing function changes the search space from subframc to subframe. This way it can be ensured that at least the same UEs are not blocking each other in the same subframe. Hashing is also illustrated in Figure 1 where it is seen that the search space locations change from subftame n to subframe n-I-I. Among other inputs, the hashing function takes as input the UE ID and the slot number within the radio frame. This ensures that the search space is UE-specitic and varies from one subframe to another.

As described in document 3GPP, TS 36.213 V9.3.O (September 2010); 3 Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-IJTRA); Physical layer procedures (Release 9), the set of PDCCH candidates to monitor are defined in terms of search spaces, where a search space at aggregation level L G {,2,4,s) is defined by a set of PDCCH candidates. The CCEs corresponding to PDCCI-I candidate in of the search space k are given by L.((1 +m)modL/VccEk /LJ)÷i where is defined below, iO,,L-1 and in=O,,M1-1 41(L) is the number of PDCCH candidates to monitor in the given search space.

As defined in the aforementioned document 3GPP, TS 36.213 V9.3.0 (September 2010); 31 Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 9), the UE shall monitor one common search space at each of the aggregation levels 4 and 8 and one UE-speeific search space at each of the aggregation levels 1, 2, 4, 8. The common and UE-specific search spaces may overlap.

For the common search spaces, is set to 0 for the two aggregation evels L = 4 and L = S ç(L) For the UE-specific search space at aggregation level L, the variable 1k is defined by where 1-1='um°, A39827, D65537 and k=k/2] istheslotnumberwithin a radio frame. The KN11 value used for is defined in the aforementioned document 3GPP, TS 36.213 V9.3.O (September 2010); 3td Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Teitestrial Radio Access (E-UTRA); Physical layer procedures (Release 9).

As mentioned above, with the enhanced PDCCH, the spatial domain with multiple spatial layers and associated UF-specific itS bring yet another dimension into the blind decoding process. On one hand the UE should not be required to estimate channels from an excessive number of difkrent tJE-spccific RS ports, but also on the other hand the scheduling should not be restricted too much by fixing the UE-specific RS port for PDCCH demodulation as such restrictions are well-known to degrade MU-MIMO performance by restricting multi-user diversity because of restrictions in UE pairing, and flirthennore the same blocking problem would arise again.

The problem addressed by the present invention is that of alleviating blocking and giving the eNB more scheduling freedom in scheduling PDCCFLs when multiple spatial layers are utilized.

The present invention refers to control signaling enhancements for LTE.

Embodiments of the invention provide an apparatus and method and a computer program product for spatial hashing for enhanced control channel search spaces.

According to an exemplary embodiment, there is provided a method of searching for channel candidates, the method comprising: defining a control channel search space for searching fbr control channel candidates, defining search space locations within the control channel search space, grouping the search space locations into a plurality of subsets of search space locations, associating each subset of search space locations with an antenna port, for each of a plurality of subframes, changing the search space locations from a first subset of search space locations to a second subset of search space locations.

According to another exemplary embodiment, therc is providcd a method of searching for channel candidates, the method comprising: defining a control channel search spacc for searching for control channel candidates, defining search space locations within the control channel search space, grouping the search space locations into N subsets of search space locations, wherein N is thc numbcr of antenna ports, associating each of thc N subscts of search space locations with one of the N antenna ports, alternating the association between each of the N subsets and said antenna port for each of thc N subframcs, changing the scarch space locations from a first subset of search space locations to a sccond subset of search spacc locations at every N subframe.

According to an exemplary embodiment, there is provided an apparatus for use in searching for channel candidates, the apparatus comprising a processing system, which may be embodicd as at least one proccssor and at least one memory including computcr program code, whcrcin the processing system is arrangcd to cause the apparatus to: define a control channel search spacc for searching for control channel candidates, define search space locations within the control channel search space, group the search space locations into a plurality of subsets of search space locations, associatc each subset of search space locations with an antenna port, for each of a plurality of subsets, changing the search space locations from a first subset of search space locations to a second subset of search space locations.

According to an exemplary embodiment, there is provided an apparatus for use in searching for channel candidates, the apparatus comprising a processing system, which may be embodied as at least one processor and at least one memory including computer program code, wherein the processing system is arranged to cause the apparatus to: dcfine a control channel scarch space for searching for control channel candidates, define search spacc locations within thc control channel search space, group the search space locations into N subsets of search space locations, wherein N is the number of antenna ports, associate each of the N subsets of search space locations with one of the N antenna ports, alternate the association between each of the N subsets and said antenna port for each of the N subframes, change the search space locations from a first subset of search space locations ot a second subset of search space locations at every N subframe.

According to an exemplary embodiment, there is provided method of in searching for channel candidates, the method comprising: defining a control channel search space for scheduling control channel candidates, defining search space locations within the control channel search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into subsets, each subset of search space locations is associated with an antenna port, and for each of a plurality of subframes, the search space locations arc changed from a first subset of search space locations to a second subset of search space locations.

According to an exemplary embodiment, there is provided method of in searching for channel candidates, the method comprising: defining a control channel search space for scheduling control channel candidates, defining search space locations within the control channel search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into N subsets of search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna ports, the association between each of the N subsets of search space locations and said antenna port for each of the N subframcs is alternated, and the search space locations are changed from a first subset of search space locations to a second subset of search space locations at every N subframe.

According to exemplary embodiment, there is provided an apparatus, comprising a processing system, which may be embodied as at least one processor and at least one memory including computer program code, wherein the processing system is arranged to cause the apparatus to: define a control channel search space for scheduling control channel candidates, define search space locations within the control channel search space, schedule one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into a plurality subsets, each subset of search space locations is associated with an antenna port, and for each of a plurality of subframcs, the search space locations arc changedfrom a first subset of search space locations to a second subset of search space locations.

According to an exemplary embodiment, thcrc is provided an apparatus, comprising a processing system, which may be embodied as at least one processor and at least one memory including computer program code, wherein the processing system is arranged to cause the apparatus to: define a control channel search space for scheduling control channel candidates, define search space locations within the control channel search space, schedule one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into N subsetsof search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna ports, the association between each of the N subsets and said antenna port for each of the N subframcs is alternated, and the search space locations arc changed from a first subset of search space locations to a second subset of search space locations at every N subframe.

Brief Description of the Drawings

The above and other objects, features, details and advantages will become more fully apparent from the following detailed description of example embodiments which is to be taken in conjunction with the appended drawings, in which: Fig. I shows an illustration of the Release 8 -type of PDCCI-1 CCE aggregation tree and the hashing function changing the search space from subframe to subframe.

Fig. 2 shows an example of a tree-structure based spatial hashing according to a first embodiment of the present invention.

Fig. 3 shows an illustration of space-time hashing according to a second embodiment of the present invention.

Fig. 4 shows an example of independent hashing for each RS port according to a third embodiment of the present invention.

Fig. 5 shows an example of independent hashing for each RS port with reduced search space according to a fourth embodiment of the present invention.

Fig. 6 shows a configuration of an example for an apparatus according to certain embodiments of the present invention.

Fig. 7 shows a flowchart of an example for a method according to certain embodiments of the present invention.

Fig. 8 shows a flowchart of another example for a method according to certain embodiments of the present invention.

Fig. 9 shows a configuration of an example for another apparatus according to certain embodiments of the present invention.

Fig. 10 shows a flowchart of an example for another method according to certain embodiments of the present invention.

Fig. 11 shows a flowchart of another example for another method according to certain embodiments of the present invention.

Detailed Description

In the following, embodiments of the present invention are described by referring to general and specific examples of the embodiments, It is to be understood, however, that the description is given by way of example only, and that the described embodiments are by no means to be understood as limiting the present invention thereto.

According to an embodiment of the present invention, a spatial component is addcd to the PDCCH hashing function. This provides randomization of the PDCCH search space in the spatial domain, and hence reduces blocking since it becomes unlikely that liEs that are spatially compatible (such that they can be paired in multi-user MIMO sense) would be allocated the same liE-specific RS port (and scrambling ID) in consecutive subframes. Hence the PDCCH scheduling with MIJ-MIMO will not be blocked in all subframes due to RS allocation. In other words, the spatial domain offers another dimension for ePDCCH multiplexing which allows increasing its capacity and reducing blocking.

As a result the dedicated RS port that liE will be searching through in the PDCCH blind decoding process will depend on the CCE and subframe numbers.

As described above, the blind decoding process amounts to decoding control channel candidates under certain hypotheses on the coding rate, resource mapping, length of the DCI format, and, according to the present invention, the UE-specific antenna port. When the cyclic redundancy check (CRC) is successful, the FE can assume that it has successfully decoded PDCCH and that the corresponding hypotheses are valid.

In the following, there are described four possible ways of implementing a spatial hashing function for ePDCCH. The starting point for the examples is Fig. 1, which illustrates the principle of the usual single RS port hashing function, as described above.

(Embodiment 1) Tree structure -based spatial hashing In the first embodiment, the spatial hashing is configured such that for each CCE the UE only needs to estimate channels from one DM-RS port. This is achieved such that the search space locations corresponding to each DM-RS port arc frilly non-overlapping. As an example, expanding the example of Fig. 1 to multiple DM-RS ports, one might assign separate parts of the overall CCE space to different DM-RS ports to achieve this. In the example of Fig. 2, the CCEs in the second half are decoded based on antenna port 7 and CCEs in the first half of the overafl CCE space are decodcd based on antenna port 8. The benefit of the method is reduced channel estimation complexity while both ports 7 and 8 are enabled at least in some part of the search space allowing flexibility for scheduling ePDCCH in MU-MIMO over orthogonal DM-RS ports.

(Embodiment 2) Space-time hashing function In the second embodiment, instead of having the search space locations changed in every subframe, as described in the first embodiment, the overall search space locations are changed only every N subframes in case N DM-RS ports are in use. Then, within the N subframes, the search space locations are alternated between the N DM-RS ports. The overall search space is split into N subsets, and in each of the N subframcs each DM-RS port is associated with a different subset of the search space locations. It is noted that the subsets are fully non-overlapping (or disjoint), as described above.

However, alternatively, it is also possible that the subsets are partially overlapping (or not disjoint).

Fig. 3 illustrates the idea with N=2. In this example, the fill search space is divided into two subsets. In subframe n, antenna port 7 is associated with the first subset and antenna port 8 with the second subset, and in subframc n+I the association is vice versa.

(Embodiment 3) Independent hashing for each DM-RS port In the third embodiment, there are separate search spaces defined for all DM-RS ports, and hashing is DM-RS port-specific. This results in completely independent search spaces associated with each DM-RS port, which is illustrated in Fig. 4.

(Embodiment 4) Independent hashing combined with reduced search space per DM-RS port In a fourth embodiment, to avoid excessive amount of blind decodings to be performed by the UE, a simplification of the method as described in the third embodiment is provided, which reduces the search space size associated with each DM-RS port. This can be done such that the overall search space size still remains the same compared to the baseline case of Fig. I, e.g. in the embodiment shown in Fig. S the overall search space sizes on aggregation levels (1,2,4,8) are still {3,3,1,1}, respectively.

According to such an approach, the amount of blind decodings at the UE is kept under control.

In the above description, different embodiments of the invention have been mentioned.

In particular, the above embodiments describe examples that involve use of a spatial hashing frmnction that randomizes the search space also across DM-RS ports. It is to be appreciated that other examples, for example, combinations of the four embodiments described above, are envisaged In the above described embodiments, a total number of two DM-RS ports is assumed, but the principles described in this invention report extend to any number of DM-RS ports.

Further, while for convenience of explanation, the Release 9/10 DM-RS terminology has been used, it is acknowledged that other type of reference symbols are suitable to this process, like e.g. reference symbols that may be liE specific prccoded or beam specific precoded.

As to the related TiE and eNB procedures according to embodiments, it is noted that the hashing function is configured such that both the eNB and the TiE have in each subframc a common understanding about the search space associated with each DM-RS port.

For example, when scheduling the cPDCCH, the eNB selects a suitable search space location where to schedule the cPDCCH for the UE. This involves at least: -Selecting the aggregation level (coding rate) based on e.g. CQI knowledge from the UE.

-Checking whether the tiE can be paired in MU-MIMO with anothcr TIE, and determining which DM-RS ports should be used for both TiEs.

-Finding a suitable search space location given the aggregation level and the DM-RS port. If there is no such location, the eNB for example tries pairing with other UEs, or uses single-user transmission instead. It should be appreciated that these three steps may need to be iterated multiple times to find the suitable search space location.

Further, when receiving ePDCCH, the tiE attempts to decode ePDCCH from each search space location, It is to be noted that: -The specified hashing function gives the information about which search space locations the TIE will need to try with each DM-RS port for channel estimation for ePDCCH demodulation in a given subframe.

-ePDCCH is detected when the CRC matches correctly.

According to certain embodiments of the present invention, there are enabled better possibilities for the eINB to perform MU-MIMO on the enhanced PDCCH, since DM-RS port allocation is made dynamic. At the same time blocking probability is kept low.

Fig. 6 shows a principle configuration of an example for an apparatus according to certain embodiments of the present invention. One option for implementing this example for an apparatus according to certain embodiments of the present invention would be a component in a handset such as user equipment tiE according to LTE.

Specifically, as shown in Fig. 6, the example for an apparatus 10 comprises at least one processor 11, and at least one memory 12 including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform defining a control channel search space for searching for control channel candidates, defining search space locations within the search space, grouping the search space locations into a plurality of subsets of search space locations, associating each subset of search space locations with an antenna port, for each of a plurality of subframes, changing the search space locations from a first subset of search space locations to a second subset of search space locations.

According to another embodiment, the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform defining a control channel search space for searching for control channel candidates, defining search space locations within the search space, grouping the search space locations into N subsets of search space locations, wherein N is the number of antenna ports, associating each of the N subsets of search space locations with one of the N antenna ports, alternating the association between each of the N subsets and said antenna port for each of the N subftames, changing the search space locations from a first subset of search space locations to a second subset of search space locations at every N subframe.

In the foregoing exemplary description of the apparatus, only the units that are relevant for understanding the principles of the invention have been described using functional blocks. The apparatus may comprise further units that are necessary for its respective operation. However, a description of these units is omitted in this specification. The arrangement of the functional blocks of the devices is not construed to limit the invention, and the functions may be performed by one block or further split into sub-blocks.

Fig. 7 shows a principle flowchart of an example for a method according to certain embodiments of the present invention. That is, as shown in Fig. 7, this method comprises defining, at step S21, a control channel search space for searching for control channel candidates, defining, at step S22, search space locations within the search space, grouping, at step S23, the search space locations into a plurality of subsets of search space locations, associating, at step S24, each subset of search space locations with an antenna port, and for each of a plurality of subframes, changing, at step S25, the search space locations from a first subset of search space locations to a second subset of search space locations.

Fig. 8 shows a principle flowchart of another example for a method according to certain embodiments of the present invention. That is, as shown in Fig. 8, this method comprises defining, at step S3 1, a control channel search space for searching for control channel candidates, defining, at step 532, search space locations within the search space, grouping, at step S33, the search space locations into N subsets of search space locations, wherein N is the number of antenna ports, associating, at step S34, each of the N subsets of search space locations with one of the N antenna ports, alternating, at step S35, the association between each of the N subsets and said antcnna port for each of the N subframes, and changing, at step 536, the search space location from a first subset of search space locations to a second subset of search space locations at every N subframes.

One option for performing the example of a method according to certain embodiments of the present invention would be to use the apparatus as described above or a modification thereof which becomes apparent from the embodiments as described above.

Fig. 9 shows another principle configuration of an example for an apparatus according to certain embodiments of the present invention. Onc option for implementing this example for an apparatus according to certain embodiments of the present invention would be a component in a base station such as an eNB according to LTE.

Specifically, as shown in Fig. 9, the example for an apparatus 40 comprises at least one processor 41, and at least one memory 42 including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform defining a control channel search space for scheduling control channels, defining search space locations within the search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into a plurality subsets, each subset of search space locations is associated with an antenna port, and for each of a p'urality of subframes, the search space locations are changed from a first subset of search space locations to a second subset of search space locations.

According to another embodiment, the at least one memory and the computer program code arc further configured to, with the at least one processor, cause the apparatus to defining a control channel search space for scheduling control channels, defining search space locations within the search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations arc grouped into N subsets of search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna ports, the association between each of the N subsets and said antenna port for each of the N subframes is alternated, the search space locations arc changed from a first subset of search space locations to a second subset of search space locations at every N sub frame.

Fig. 10 shows a principle flowchart of an example for a method according to certain embodiments of the present invention. That is, as shown in Fig. 10, this method comprises defining, at step S51, a control channel search space for scheduling control channels, defining, at step S52, search space locations within the search space, and scheduling, at step S53, one or a plurality of control channels in the defined search space locations, wherein the search space is grouped into subsets, each subset of search space locations is associated with an antenna port, and for each of a plurality of subframes, the search space locations are changed from a first subset of search space locations to a second subset of search space locations.

Fig. 11 shows a principle flowchart of another example for a method according to certain embodiments of the present invention. That is, as shown in Fig. 11, this method comprises defining, at step S61, a control channel search space for scheduling control channels, defining, at step S62, search space locations within the search space, and scheduling, at step S63, one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into N subsets of search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna pods, the association between each of the N subsets of search space locations and said antenna port for each of the N subframcs is alternated, and the search space locations are changed from a first subset of search space locations to a second subset of search space locations.

One option for performing the example of a method according to certain embodiments of the present invention would be to use the apparatus as described above or a modification thereof which becomes apparent from the embodiments as described abovc.

It is noted that in each of the above described embodiment, the search space locations corresponding to each antenna port are partially overlapping or fully non-overlapping.

For the purpose of the present invention as described herein above, it should be noted that -method steps likely to be implemented as software code portions and being run using a processor at a user equipment (as examples of devices, apparatuses and/or modules thereof; or as examples of entities including apparatuses and/or modules thcreforc), arc software code independent and can be specified using any known or future developed programming language as long as the frmnctionality defined by the method steps is preserved; -generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the embodiments and its modification in terms of the functionality implemented; -method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module(s) thereof; (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components; -devices, units or means (e.g. the above-defined apparatuses and user equipments, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved; -an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude thc possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for executionibeing run on a processor; -a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

In general, it is to be noted that respective functional blocks or elements according to above-described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual function& Mocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles arc to be considered as known to a skilled person.

Software in the sense of the present description comprises software code as such comprising code means or portions or a computer program or a computer program product for performing the respective functions, as well as software (or a computer program or a computer program product) embodied on a tangible medium such as a computer-readable (storage) medium having stored thereon a respective data structure or codc means/portions or embodied in a signal or in a chip, potentially during processing thereof It is noted that the embodiments and general and specific examples described above are provided for illustrative purposes only and are in no way intended that the present invention is restricted thereto. Rather, it is the intention that all variations and modifications which fall within the scope of the appended claims are covered.

Claims

<claim-text>Claims A method of searching for channel candidates, the method comprising: defining a control channel search space for searching for control channel candidates, defining search space locations within the control channel search space, grouping the search space locations into a plurahty of subsets of search space locations, associating each subset of search space locations with an antenna port, for each of a plurality of subframes, changing the search space locations from a first subset of search space locations to a second subset of search space locations.</claim-text> <claim-text>2. The method according to claim 1, further comprising decoding the control channel candidates from the defined search space locations.</claim-text> <claim-text>3. The method according to claim 1, wherein the subsets of search space locations corresponding to each anteima port are partially overlapping or fliHy non-overlapping.</claim-text> <claim-text>4. The method according to claim 1, further comprising: defining separate search space locations within the search space for each antenna port, changing the subset of search space locations for one antenna port independently of the subset of search space locations for another antenna port.</claim-text> <claim-text>5. The method according to claim 4, further comprising: reducing the number of search space locations in a subset for each antenna port.</claim-text> <claim-text>6. A method of searching for channel candidates, the method comprising: defining a control channel search space for searching for control channel candidates, defining search space locations within the control channel search space, grouping the search space locations into N subsets of search space locations, wherein N is the number of antenna ports, associating each of the N subsets of search space locations with one of the N antenna ports, alternating the association between each of the N subsets and said antenna port for each of the N subframes, changing the search space locations from a first subset of search space locations to a second subset of search space locations at every N subframc.</claim-text> <claim-text>7. The method according to claim 6, wherein the subsets of search space locations corresponding to each antcnaa port are partially overlapping or fully non-overlapping.</claim-text> <claim-text>8. The method according to claim 6, further comprising decoding the control channel candidates from the defined search space locations.</claim-text> <claim-text>9. An apparatus for use in searching for channel candidates, the apparatus comprising a processing system arranged to cause the apparatus to: define a control channel search space for searching for control channel candidates, define search space locations within the control channel search space, group the search space locations into a plurality of subsets of search space locations, associate each subset of search space locations with an antenna port, for each of a plurality of subsets, change the search space locations from a first subset of search space locations to a second subset of search space locations.</claim-text> <claim-text>10. The apparatus according to claim 9, wherein the subsets of search space locations corresponding to each antenna port arc partially overlapping or frilly non-overlapping.</claim-text> <claim-text>11. The apparatus according to claim 9, wherein the processing system is arranged to cause the apparatus to: define separate search spacc locations within the search space for each antenna port, change the subset of search space locations for one antenna port independently of the subset of search space locations for another antenna port.</claim-text> <claim-text>12. The apparatus according to claim 11, wherein the processing system is arranged to cause the apparatus to: reduce the number of search space locations in a subset for each antenna port.</claim-text> <claim-text>13. The apparatus according to claim 9, wherein the processing system is arranged to cause the apparatus to: decode the control channel candidates from the defined search space locations.</claim-text> <claim-text>14. An apparatus for use in searching for channel candidates, the apparatus comprising a processing system arranged to cause the apparatus to: define a control channel search space for searching for control channel candidates, define search space locations within the control channel search space, group the search space locations into N subsets of search space locations, wherein N is the number of antenna ports, associate each of the N subsets of search space locations with one of the N antenna ports, alternate the association between each of the N subsets and said antenna port for each of the N subframcs, change the search space locations from a first subset of search space locations to a second subset of search space locations at every N subframe.</claim-text> <claim-text>15. The apparatus according to claim 14, wherein the subsets of search space ocations corresponding to each antenna port are partially ovcdapping or frilly non-overlapping.</claim-text> <claim-text>16. The apparatus according to claim 14, wherein the processing system is arranged to cause the apparatus to: decode the control channel candidates from the defined search space locations.</claim-text> <claim-text>17. A method of searching for channel candidates, the method comprising: defining a control channel search space for scheduling control channels, defining search space locations within the control channel search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into subsets, each subset of search space locations is associated with an antenna port, and for each of a plurality of subframes, the search space locations are changed from a first subset of search space locations to a second subset of search space locations.</claim-text> <claim-text>18. The method according to claim 17, wherein the search space locations corresponding to each antenna port are partially overlapping or fully non-overlapping.</claim-text> <claim-text>19. The method according to claim 17, further comprising: defining separate search space locations within the search space for each antenna port, changing the subset of search space Locations for one antenna port independently of the subset of search space locations for another antenna port.</claim-text> <claim-text>20. The method according to claim 19, further comprising: reducing the number of search space locations in a subset for each antenna port.</claim-text> <claim-text>21. A method of searching for channel candidates, the method comprising: defining a control channel search space for scheduling control channels, defining search space locations within the control channel search space, scheduling one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into N subsets of search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna ports, the association between each of the N subsets of search space locations and said antenna port for each of the N subframes is alternated, and the search space locations are changed from a first subset of search space locations to a second subset of search space locations at every N subframe.</claim-text> <claim-text>22. The method according to claim 21, wherein the subsets of search space locations corresponding to each antenna port are partially overlapping or fully non-overlapping.</claim-text> <claim-text>23. An apparatus for use in searching for channel candidates, the apparatus comprising a processing system arranged to cause the apparatus to: define a control channel search space for scheduling control channels, define search space locations within the control channel search space, schedule one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into a plurality subsets, each subset of search space locations is associated with an antenna port, and for each of a plurality of subframcs, the search space locations are ehangedfrom a first subset of search space locations to a second subset of search space locations.</claim-text> <claim-text>24. The apparatus according to claim 23, wherein the subsets of search space locations corresponding to each antenna port are partially overlapping or frilly non-overlapping.</claim-text> <claim-text>25. The apparatus according to claim 23, wherein the processing system is arranged to cause the apparatus to: define separate search space locations within the search space for each antenna port, change the subset of search space locations for one antenna port independently of the subset of search space locations for another antenna port.</claim-text> <claim-text>26. The apparatus according to claim 25, wherein the processing system is arranged to cause the apparatus to: reduce the number of search space locations in a subset for each antenna port.</claim-text> <claim-text>27. An apparatus for usc in searching for channel candidates, the apparatus comprising a processing system arranged to cause the apparatus to: define a control channel search space for scheduling control channels, define search space locations within the control channel search space, schedule one or a plurality of control channels in the defined search space locations, wherein the search space locations are grouped into N subsetsof search space locations, wherein N is the number of antenna ports, each of the N subsets of search space locations is associated with one of the N antenna ports, the association between each of the N subsets and said antenna port for each of the N subframcs is alternated, and the search space locations arc changed from a first subset of search space locations to a second subset of search space locations at every N subframc.</claim-text> <claim-text>28. The apparatus according to claim 27, wherein the subsets of search space locations corresponding to each antenna port are partially overlapping or frilly non-overlapping.</claim-text> <claim-text>29. A computer program, or a suite of computer programs, comprising a set of instructions, which, when executed by a computing device, causes the computing device to perform the steps of: defining a control channel search space for searching for control channel candidates, defining search space locations within the control channel search space, grouping the search space locations into a plurality of subsets of search space locations, associating each subset of search space locations with an antenna port, for each of a plurality of subframcs, changing the search space locations from a first subset of search space locations to a second subset of search space locations</claim-text>