GB2542611A - Wireless communication system devices - Google Patents

Abstract

A Down Link control signalling Physical layer enhancement allows for a wireless network to send additional information to a wireless communication device (102) in connected mode in order to reduce the number of Blind Decodes the device has to perform over the physical downlink control channel PDCCH to find its Downlink Control Information DCI within a subframe. An auxillary DCI message is generated by an eNodeB for transmission to a User Equipment. The auxillary DCI message may contain information including the DCI format, the Aggregation Level and the Control Channel Element CCE index number, This information is used by the UE to reduce the search space for the conventional DCI messages and therefore reduce the number of blind decodes needed.

Description

WIRELESS COMMUNICATION SYSTEM DEVICES TECHNICAL FIELD

[0001] Embodiments of the present invention generally relate to wireless communication system devices and in particular to devices and methods for decoding a Downlink Channel Information (DCI) message in a wireless communication system.

BACKGROUND

[0002] Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project. The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs) to communicate with wireless communication units within a relatively large geographical coverage area. Typically, wireless communication units, or User Equipment (UEs) as they are often referred to, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more Node Bs. Communications systems and networks have developed towards a broadband and mobile system. The 3rd Generation Partnership Project has developed a Long Term Evolution (LTE) solution, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core (EPC), for a mobile core network. A macrocell in an LTE system is supported by a base station known as an eNodeB or eNB (evolved Node B).

[0003] In LTE systems, in order to support the transmission of downlink (DL) and uplink (UP) transport channels Downlink Shared Channel and Uplink Shared Channel control signalling is required. This control signalling enables a UE to successfully receive, demodulate, and decode the shared channel. Downlink Control Information (DCI) is transmitted through a Physical Downlink Control Channel (PDCCH) and includes, inter alia, information about the shared channel resource allocation and information related to the shared channel Hybrid Automatic Repeat reQuest (HARQ). A PDCCH payload, configured by the eNodeB, comprises coded DCI bits which are mapped to Control Channel Elements (CCEs) according to the PDCCH format. At the UE, after performing operations such as symbol demodulation and descrambling, the UE is required to perform the so-called ‘blind decoding’ of the PDCCH payload as it is not aware of the detailed control channel structure, including the number of control channels and the number of CCEs to which each control channel is mapped. Multiple PDCCHs can be transmitted in a single subframe which may and may not be all relevant to a particular UE.

[0004] A UE is only informed of the number of OFDM symbols within the control region of a subframe and is not provided with the location of its corresponding PDCCH. The UE uses blind decoding to find its PDCCH by monitoring a set of PDCCH candidates (or target DCIs) in every subframe. In a conventional method, the UE is not aware of the location of its PDCCH(s)/DCI(s) in each Component Carrier’s search space (SS) and has to find it by monitoring a set of possible candidates/targets in every subframe for each Component Carrier (CC). More specifically, the UE has no information about either the Aggregation Level (AL) used by the eNodeB, the DCI Format used by the eNodeB or the specific CCEs used for the UEs PDCCH placed in a Component Carrier’s search space (CC SS). Therefore, the maximum number of blind decodes that a UE has to perform depends on how many and which Aggregation Levels and how many DCI Formats are supported by the eNodeB for a specific CC SS. A number of PDCCH candidates can be evaluated by the UE by knowing the number of Aggregation Levels supported by the CC; and this information is generally made known to the UE at Component Carrier configuration. Moreover, the exact possible locations (ie. starting CCE index) of its PDCCH can be calculated for the UE Search Space (USS) based on its Radio Network Temporary Identity (RNTI) number used and the index of the current subframe to successfully find its DCI(s) in that subframe, while for the Common Search Space (CSS) it is fixed. That is to say that additional information (apart from the AL) is required to find the exact starting CCE index (as will be appreciated by those familiar with the relevant standards). Finally, the UE has to try and blindly decode each DCI candidate, i.e. each PDCCH candidate for all DCI Formats supported by the CC, which is again made known at CC configuration. There are proposals to enhance LTE Carrier Aggregation beyond five carriers, as is currently the case, up to a maximum of 32. This would significantly increase the number of blind decodes that a UE would have to do in order to find its PDCCH and retrieve its Downlink Control Information. In particular, the number of necessary USS blind decodes increases linearly with the number of configured Component Carriers. This would place an additional burden on the UE and in particular, could have a deleterious effect on its ability to perform channel decoding with a 3ms gap for the corresponding HARQ feedback. An increase in false alarm probability also affects system operation. Therefore, it would be advantageous to provide a means of ameliorating the above foreseen problems.

[0005] The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known systems.

SUMMARY

[0006] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0007] According to a first aspect of the present invention, there is provided a method for decoding a Downlink Control Information (DCI) message in a wireless communication device in a wireless communication system, the method comprising; in a wireless communication unit of the wireless communication system, generating and transmitting a Physical Downlink Control Channel (PDCCH) payload for reception by the wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message.

[0008] According to a second aspect of the invention, there is provided a processing module for a wireless communication unit for generating, for transmission by the wireless communication unit, a Physical Downlink Control Channel (PDCCH) payload for reception by a wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message.

[0009] In one example, the information relates to the location of the PDCCH that the DCI message has been mapped onto.

[0010] The method can be used for User Specific Search Space or Common Search Space.

[0011] The auxiliary DCI message may also include the DCI format of the DCI message or another DCI message.

[0012] The auxiliary DCI message can provide information about the DCI message in the same or different CC PDCCH payload. For example, a wireless communication unit can send to a wireless communication device via CC#1 a DCI#1 and an auxiliary DCI and via CC#2, a DCI#2. The auxiliary DCI can have information for finding faster either or both DCI#1 or/and DCI#2.

[0013] The wireless communication system may be an LTE system.

[0014] The wireless communication unit may be a base station such as an eNodeB, for example.

[0015] According to a third aspect of the invention there is provided a signal processor for a wireless communication device for receiving a Physical Downlink Control Channel (PDCCH) payload transmitted by a wireless communication unit for reception by the wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message, and for decoding a DCI message using the information included in the auxiliary DCI message.

[0016] The wireless communication device may be a User Equipment or similar mobile communications device. The UE may be in connected mode when receiving the PDCCH payload. The UE may have CA capability.

[0017] Hence, a Down Link control signalling Physical layer enhancement is introduced to allow for a communications network to send additional information to a UE. This has the advantageous effect of reducing the number of Blind Decodes that UE has to perform at physical downlink control channel level to find its DCI(s) within a subframe as compared with conventional techniques.

[0018] According to a fourth aspect of the invention, there is provided a non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to the first aspect.

[0019] Provision of the auxiliary DCI message (denoted as aDCI hereafter) contains information for effectively reducing the search space of another DCI.

The UE, upon decoding an aDCI, is able to reduce (even eliminate to one) the decoding times for target DCI(s) and the total maximum number of Blind Decodes a UE has to perform within a subframe can be therefore reduced.

[0020] In one embodiment, the processing module of the wireless communication unit (e.g. an eNodeB) may also be able to regularly monitor the serving UE Blind Decoding capability and/or load at control channel level, and upon identification of an expected high number of BDs may dynamically create one or multiple aDCIs for reducing Blind Decode requirements for UEs.

[0021] With the creation of one or more aDCIs, the information elements included into an aDCI related to the decision of the target DCIs, as well as the process for ensuring reduced overall decoding time at UE, can be performed with several alternating and complementing methods.

[0022] One possible way to introduce the aDCI is to consider it as a new information field with the legacy DCI messages in current use. That is to say that the aCDI is combined with the legacy DCI content within the PDCCH. Thus, the PDCCH will be designed to consist of two parts: aDCI and legacy-DCI. This approach has the benefit of not introducing a new DCI format into the current standard.

[0023] Another possible way to introduce the aDCI is to include all auxiliary information into a new DCI format. This approach has the benefit that the total payload of any DCI can be kept at reasonable levels. As will be explained below, the maximum total size of aDCI message results into a ‘small’ or ‘normal’ DCI size.

[0024] In some embodiments, the auxiliary DCI includes information comprising at least one of; the specific Aggregation Level, the specific DCI Format, the specific starting location (i.e. CCE index) of a target DCI.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will be described, by way of example, with reference to the following drawings, in which: [0026] Figure 1 is a schematic block diagram of a wireless communication system in accordance with an embodiment of the invention; and [0027] Figure 2 is a simplified flowchart illustrating a method of decoding Downlink Control Information messages in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Embodiments of the present invention are described below by way of example only. These examples represent the best ways of putting the invention into practice that are currently known to the Applicant although they are not the only ways in which this could be achieved. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0029] Referring to figure 1, an eNodeB 101 communicates over an air interface with a User Equipment 102. The eNodeB 101 includes a processing module 103 which generates a Physical Downlink Control Channel (PDCCH) payload which includes a DCI message and an enhanced DCI message. The eNodeB transmits the PDCCH payload along with other conventional signalling and transmissions.

The User Equipment 102 includes a signal processor 104 which decodes DCI messages received in the PDCCH payload from the eNodeB 101 in a manner to be described below.

[0030] In general, there is one UE-specific search space (USS) for each Component Carrier (CC) while a common search space (CSS) exist in fewer (usually one or two) CCs. Since, USS only increases linearly with the number of CCs, the embodiment described herebelow is with reference to finding DCIs in USS. However, it will be understood that the methods disclosed are equally and straightforwardly applicable for CSS as well.

[0031] As mentioned above, as the number of activated CCs for a UE increases (up to 32 for eCA), the maximum total number of Blind Decodes the UE has to perform per subframe increases in an almost linear manner. With current operation, considering one CSS (ALs 4/8 and 2 DCI Formats supported) and x USS for x serving CCs in SU ΜΙΜΟ TM (ALs 1/2/4/8 and 3 DCI formats supported), the maximum decoding tries for the UE rise from 12 + 5*48 = 252 BDs in the 5CC case, to 12 + 32*48 = 1548 Blind Decodes in the 32CC case, i.e. ~6.1 times more. Instead of trying to decode each DCI candidate independently from each other, some useful information could be introduced in an enhanced DCI message carried within the same subframe so as, when it is decoded, the search space for finding another target DCI(s) can be reduced. Using this general two-step method, the total maximum number of Blind Decodes per subframe per UE can be reduced.

[0032] Referring now to the simplified flowchart of figure 2, steps 201 to 208 are performed in the processing module103 in the eNodeB (or eNB) 101 of figure 1. Steps 201 to 204 are conventional and relate to a target DCI. At 201 the total number of Control Channel Elements (CCE) which are available for PDCCH allocation for (Component Carrier) CC#x are found. At 202 a DCI message for CC#x is generated. (The DCI format is decided here) At 203 a total number of CCEs for the DCI message is found. (Aggregation Level decided). At 204 a starting CCE index is decided (CCE index value). Steps 205 to 208 relate to the auxiliary DCI. At 205, the total number of CCEs which are available for PDCCH allocation for CC#y are found. At 206, a DCI message for CC#y is generated. Also generated is an auxiliary DCI message for a target DCI which, the message including in this example, the DCI format (from step 202), the AL (from step 203) and the CCE index value (from step 204). At 207, a total number of CCEs for the DCI and aDCI messages is found. At 208, the staring CCE index is decided. Both DCI and aDCI messages are then transmitted to the UE. It will be appreciated that CC#x and CC#y can be the same CC and that CC#x and CC#y can regard different subframes. .

[0033] Steps 209 to 215 are performed in the signal processor 104 of the UE 102. Steps 210, 211 and 215 are conventional. The PDCCH payload which includes the DCI message and the aDCI message is received at the UE. At 209, the received aDCI at CC#y PDCCH is decoded in a first step (or phase) in subframe n. A second step (or phase) commences at 210, (subframe n+k, where can be greater than or equal to zero) where the total number of CCEs used for CC#x PDCCH is found.. At 211, a search in the CSS or USS is performed. After 211, the method may progress to 211, or jump to 213,214 or 215. For example, if the aDCI contains information about specific AL used, then step 212 will be skipped. If aDCI contains information about starting CCE index, then step 213 will be skipped. If aDCI contains information about specific DCI format, step 214 will be skipped. DCI candidate is found using the auxiliary information provided by aDCI. The aDCI can contain any one or any combination of the above information. At 212, a PDCCH: candidate is found. . At 213, a starting CCE index is found. . At 214, a DCI candidate is found. At 215, an attempt is made to decode the DCI found candidate. Reference 216 depicts the reduced search space which can result from using the method of figure 2, resulting in a fewer number of Blind Decodes (BDs) per subframe compared with conventional methods [0034] By using a two-phase method for decoding DCI, the second phase, after aDCI is successfully decoded (207), becomes faster than the current DCI decoding operation. Preferably, the first phase (206, 207) processing time should be kept at low levels so that the overall operation is quicker than the legacy one in case they occur in the same subframe. For the general case, still faster decoding operation of an aDCI will lighten the processing burden of the UE.

[0035] In one example, the aDCI is never placed in a higher Aggregation Levels and therefore have less Blind Decodes, in such a case there will be a tradeoff with the probability of correctly decoding an aDCI which has to be taken into account upon implementation as failing to decode the aDCI would result into no faster operation at the second phase (208-211).In general, a small size aDCI should allow for robust encoding even with smaller AL.

[0036] Another option is to limit the aDCI Blind Decodes by specifying that a UE configured with a high number of CCs should always look for aDCI only and never look for one of the legacy DCI formats until the second phase of the decoding.

[0037] An alternative approach is to combine aDCI with the Part-I consisting DCI Format Index of the PDCCH design. The extended aDCI can be encoded by a simple Forward Error Correction scheme which has both error-correcting and error-detecting capabilities. Thus, no convolutional coding imposing high computation needs is applied and scrambled by part or all UE-specific RNTI (depending on if the aDCI is part of a legacy DCI or standalone) so a UE can quickly decode it during the first phase.

[0038] It is possible for the total number of CCs to be divided into groups where each group has a primary CC. In that case, the aDCI can be sent only on primary CC (if one or more other CCs in the group include allocation in the particular SubFrame). An aDCI points to a group of target DCIs in this approach. There are two possible cases for the group of CCs: In a first case, all CCs are using the same AL. This for example can be the case where CCs are co-located and since the channel conditions are similar between UE and all of the CCs, the AL can be either signalled or extracted implicitly for all of them by just, for example, blindly decoding first the search space of the primary cell. In a second case, the AL of CCs is not the same, therefore needing to be signalled per CC. Thus, assuming for example a maximum, of 8 CCs per group, one can consider a bit map of CCs. Each field in the bit-map can be of 2-7 bits, indicating one or a combination of the following information: AL: if group AL definition is not possible, 2 bits will be needed for every CC. Otherwise, only 2 bits will be needed in total to define the AL used in the group; DCII format:: 2 bits will be needed to cover the DCI sizes supported for a TM plus the fallback TM DCI format. CCE index: Considering that AL is already known at the UE, a maximum of 6 PDCCH candidates exist for any AL. In general, an extended CCE index field could be considered to also cover the case where AL is not known. In that case, the field size will depend on the maximum possible number of CCEs. However, considering USS of a CC, 9 bits will be needed to cover the maximum possible number of CCE indexes(with 20MHz, 4 antennas, 3 PDCCH OFDM symbols) and this would add bigger payload compared to the 2+3=5 bits in case both AL and CCE index are provided together which will have the same effect BDs number reduction. , Where AL is known, 3 bits could indicate the exact CCE index and also the option of “no allocation on this CC”. This option could also be denoted by a separate information element bit in order to be able to always receive this information regardless if CCE index information element is included in aDCI or not.

The maximum total size of the aDCI (not considering the 1 extra bit which could be needed on top of the bit-map to denote if the group of CCs is using the same AL or not) is 2 + 5*8 = 40 bits in the first case where all CCs use the same AL or 7*8 = 56 bits in the second case where the AL of CCs is not the same. In general, this could be considered a ‘small’ to ‘normal’ DCI size.

[0039] The following table shows some exemplary values for a specific scenario using a grouped approach and illustrating the benefits (in terms of reduction in number of maximum Blind Decodes required per UE per SF per group of CCs) as well as the introduced signalling overhead (in terms of aDCI size). The specific scenario assumes; 8 CCs group, 1 CSS in the group, aDCI only for USS, UL ΜΙΜΟ TM, 1 DCI per CC per UE.

An alternative approach is to have aDCIs that provide pointing information to a single target DCI rather than a group of target DCIs. In this approach, any CC (not only a primary) can carry aDCI for a UE. In fact, an aDCII can be carried via any CC control channel and can help decoding one or multiple target DCIs at any CC. The maximum total additional signalling in PDCCH of all CCs will then be similar to the aforementioned approach. However, in that case, a huge payload size of a single DCI is avoided since only a 2-7 bit information field (for AL , DCI Format and/or CCE index) needs to be added to each CC DCI. A bit-map for indicating the CC of the target DCI will not be needed as this information can be implicitly provided to a UE, e.g. by using the order of CC configuration/activation. Thus, both aDCI and target DCI can be sent on a known-n-advance CC to the UE. This alternative approach can be especially useful in the case where aDCI is within a legacy DCI since the 7-bit maximum aDCI size should not add a significant payload burden to legacy DCIs. Implementation issues at the eNodeB and UE side can be checked in order to make sure that no scheduling or latency restrictions are imposed by having to consecutively decode aDCIs..

Those skilled in the art will appreciate that there will be two ways of scheduling in eCA; Self-scheduling and cross-scheduling. The first one is the legacy one where each CC schedules itself, i.e. the DCI carried in its PDCCH payload refers to resource allocations to PDSCH/PUSCH payload of the same CC. CA Crosscarrier scheduling refers to the case where a CC can schedule also other CCs. The methods disclosed herein advantageously apply to both cases. Further, the methods provide additional flexibility in case decoding time in the UE is an issue. There is the case that the UE may not have time (or buffer) to wait for this first decoding of aDCI to address the target DCI coming e.g. on the other CC at the same subframe (and the invention still provides efficient solutions in the subcase that aDCI and target DCI are received at the same subframe). So, optionally, the aDCI is arranged to point on DCI at a future subframe. In a specific case, the aDCI provides pointing information to a single target DCI for current CC or CC arriving in the n+k subframe (n = current subframe when aDCI is received at UE)

Further examples of possible fields which can be inside a aDCI are; whether there is DCI allocation in the target CC ; the number of DCIs to be received through the target CC for the UE; whether the group of CCs is using the same AL or not.

In other examples, aDCI can be further combined with a CRC to decrease the probability of false detection, or erroneous decoding.

In another example, aDCI provides pointing information to multiple target DCIs (to be) received through the same CC.

The aDCI and target DCI could be in different subframes

The auxiliary CC and the target CC could belong to different eNodeBs.

Different eNodeBs could exchange scheduling information between them so as they know UE-related instantaneous configurations (e.g. AL, DCI Format etc) in order to create aDCIs for target DCI in different eNodeB CC. Again aDCI and target DCI could be in different subframes.

[0040]The signal processing functionality of the embodiments of the invention, particularly the processing module 103 and signal processor 104 may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used.

[0041] The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control processor. The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor.

[0042] The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor. The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive.

[0043] Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein. In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

[0044] In this document, the terms ‘computer program product’, ‘computer-readable medium’ and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as ‘computer program code’ (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so. In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein. Further, the inventive concept can be applied to any circuit for performing signal processing functionality within a communications network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

[0045] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages.

[0046] Any reference to 'an' item refers to one or more of those items. The term 'comprising' is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0047] The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

[0048] It will be understood that the above description of a preferred embodiment is given by way of example only and that various modifications may be made by those skilled in the art. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention.

Claims (15)

1. A method for decoding a Downlink Control Information (DCI) message in a wireless communication device in a wireless communication system, the method comprising; in a wireless communication unit of the wireless communication system, generating and transmitting a Physical Downlink Control Channel (PDCCH) payload for reception by the wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message.

2. The method of claim 1 wherein the PDCCH comprises two parts, one relating to the DCI message and one relating to the auxiliary DCI message.

3. The method of claim 1 wherein the auxiliary DCI message is included with the DCI message in a revised DCI format.

4. The method of any preceding the claim wherein the auxiliary DCI message includes at least one of the following; Aggregation Levels, DCI format, Control Channel Elements (CCE) index.

5. The method of any preceding claim wherein the auxiliary DCI message is encoded using a Forward Error Correction scheme. .

6. The method of any preceding claim comprising transmitting the auxiliary DCI message only on a primary component carrier (CC) of a group of component carriers.

7. The method of any preceding claim wherein the auxiliary DCI provides pointing information to a single target DCI.

8. A processing module for a wireless communication unit for generating, for transmission by the wireless communication unit, a Physical Downlink Control Channel (PDCCH) payload for reception by a wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message.

9. The processing module of claim 8 further arranged to monitor a blind decoding activity level of the wireless communication device and to create multiple auxiliary DCI messages for transmission thereto on detection of a number of blind decodes performed by the wireless communication device exceeding a predetermined number.

9. An eNodeB comprising the processing module of claim 8 or claim 9.

10. A signal processor for a wireless communication device for receiving a Physical Downlink Control Channel (PDCCH) payload transmitted by a wireless communication unit for reception by the wireless communication device, wherein the payload comprises a DCI message and an auxiliary DCI message, the auxiliary DCI message including information relating to a location, in a Search Space, of another DCI message, and for decoding a DCI message using the information included in the auxiliary DCI message.

11. The signal processor of claim 11 arranged to search for a DCI message and decode an auxiliary DCI message in a first phase and search for and decode another DCI message in a second phase.

12. The signal processor of claim 11 arranged to only decode an auxiliary DCI message and to search for and decode a DCI message in the second phase.

13. A wireless communication device including the signal processor of any of claims 10 to 12 and arranged to receive the PDCCH payload when in a connected mode.

14. The wireless communication device of claim 13 having Carrier Aggregation capability.

15. A non-transitory computer readable medium having computer readable instructions stored thereon for execution by a processor to perform the method according to claim 1.