WO2022028588A1

WO2022028588A1 - Coverage recovery in reduced capability wireless devices

Info

Publication number: WO2022028588A1
Application number: PCT/CN2021/111240
Authority: WO
Inventors: Sebastian Wagner
Original assignee: Huizhou Tcl Cloud Internet Corporation Technology Co., Ltd.
Priority date: 2020-08-07
Filing date: 2021-08-06
Publication date: 2022-02-10
Also published as: CN116250202A

Abstract

In addition to a main CORESET for the transmission of control information in a cellular communications system a extension CORESET is defined in which control channels can be transmitted. Candidates are defined in both CORESETs and are mapped together.

Description

Coverage Recovery in Reduced Capability Wireless Devices

Technical Field

The following disclosure relates to wireless communications, and more particularly to coverage enhancements in reduced capability (REDCAP) wireless communication devices.

Background

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 (3GPP) (RTM) . The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

In cellular wireless communication systems User Equipment (UE) is connected by a wireless link to a Radio Access Network (RAN) . The RAN comprises a set of base stations which provide wireless links to the UEs located in cells covered by the base station, and an interface to a Core Network (CN) which provides overall network control. As will be appreciated the RAN and CN each conduct respective functions in relation to the overall network. For convenience the term cellular network will be used to refer to the combined RAN &CN, and it will be understood that the term is used to refer to the respective system for performing the disclosed function.

The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN) , for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB) . More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a gNB. NR is proposed to utilise an Orthogonal Frequency Division Multiplexed (OFDM) physical transmission format.

The NR protocols are intended to offer options for operating in unlicensed radio bands, to be known as NR-U. When operating in an unlicensed radio band the gNB and UE must compete with other devices for physical medium/resource access. For example, Wi-Fi (RTM) , NR-U, and LAA may utilise the same physical resources.

A trend in wireless communications is towards the provision of lower latency and higher reliability services. For example, NR is intended to support Ultra-reliable and low-latency communications (URLLC) and massive Machine-Type Communications (mMTC) are intended to provide low latency and high reliability for small packet sizes (typically 32 bytes) . A user-plane latency of 1ms has been proposed with a reliability of 99.99999%, and at the physical layer a packet loss rate of 10 ^-5 or 10 ^-6 has been proposed.

mMTC services are intended to support a large number of devices over a long life-time with highly energy efficient communication channels, where transmission of data to and from each device occurs sporadically and infrequently. For example, a cell may be expected to support many thousands of devices.

The disclosure below relates to various improvements to cellular wireless communications systems.

Summary

The invention is defined by the claims in which there is provided a method of transmitting downlink control information from a base station to a UE in a cellular communications network utilising an OFDM transmission format, the method comprising: defining a main CORESET comprising a plurality of PDCCH candidates; defininga CORESET extension including a plurality of PDCCH candidates; mapping at least one of the plurality of PDCCH candidates in the CORESET extension to at least one of the plurality PDCCH candidates in the main CORESET.

The plurality of PDCCH candidates in the CORESET extension may be mapped to a fraction of the plurality of PDCCH candidates in the main CORESET.

An offset parameter may indicate an offset applied to the CORESET extension.

The main CORESET and the CORESET extension may be interleaved before transmission.

The mapping step may use a configurable mapping or an implicit mapping.

A PDCCH candidate may be encoded and mapped onto a CCE, and wherein the UE uses at least one CCE in the main CORESET and at least one CCE in CORESET extension to decode a PDCCH candidate.

The method may further comprise: determining an aggregation level and assigning the aggregation level to the UE; generating a DCI payload; attaching a CRC to the DCI payload; encoding the DCI payload and CRC to generate a codeword; rate matching the codeword to produce a channel coding using the demodulation reference signal; scrambling and mapping the channel coding to a plurality of QPSK symbols; mapping the QPSK symbols to at least one CCE and at least one REG, using a mapping scheme defined in the main CORESET; using the at least one CCE and the at least one REG in the main CORESET.

The at least one REG in the main CORESET may be indexed independently from a second at least one REG used in the CORESET extension.

There is also provided a base station configured to perform the methoddescribed herein.

There is also provided a UE configured to decode the main CORESETand the CORESET extensionas described herein.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

Figure 1 shows selected elements of a cellular communications network;

Figures 2 to 7 show various CORESET examples that may be used in the cellular communications network of figure 1.

Detailed description of the preferred embodiments

Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

Figure 1 shows a schematic diagram of three base stations (for example, eNB or gNBs depending on the particular cellular standard and terminology) forming a cellular network. Typically, each of the base stations will be deployed by one cellular network operator to provide geographic coverage for UEs in the area. The base stations form a Radio Area Network (RAN) . Each base station provides wireless coverage for UEs in its area or cell. The base stations are interconnected via the X2 interface and are connected to the core network via the S1 interface. As will be appreciated only basic details are shown for the purposes of exemplifying the key features of a cellular network. A PC5 interface is provided between UEs for SideLink (SL) communications. The interface and component names mentioned in relation to Figure 1 are used for example only and different systems, operating to the same principles, may use different nomenclature.

The base stations each comprise hardware and software to implement the RAN’s functionality, including communications with the core network and other base stations, carriage of control and data signals between the core network and UEs, and maintaining wireless communications with UEs associated with each base station. The core network comprises hardware and software to implement the network functionality, such as overall network management and control, and routing of calls and data.

The base station transmits physical downlink control channel (PDCCH) over a pre-configured region of the time frequency grid, known as control resource set (CORESET) . A search space provides a configuration associated to a given CORESET and specifies symbols and physical resource blocks (PRBs) used by a UE to attempt PDCCH decoding. Modern Telecommunications standards include functionality for reduced capability (REDCAP) devices that operate at a reduced bandwidth as well as a reduced number of receive chains (1 RX or 2RX) .

REDCAP devices have fixed coverage loss due to hardware complexity reduction compared with standard UE devices REDCAP devices have reduced physical downlink control channel (PDCCH) monitoring capabilities and reduced bandwidth reception capacity for PDCCH. Coverage recovery solutions which require a larger bandwidth for PDCCH or an increase in the number of blind decoding attempts are not appropriate.

Solutions that can increase PDCCH coverage may reduce the Downlink Channel Information (DCI) size, giving smaller payload, which results in a higher coding rate for the same amount of resources. Other solutions may include larger aggregation levels (AL) , which can result in higher coding rate but also requires more resources which can in turn lead to PDCCH blocking. That is, not enough resources are available to schedule other UEs. Additionally, solutions may include repetition of the PDCCH, which is repeated multiple times in the time and/or frequency domain. However, for REDCAP only time-domain repetition may be an option since bandwidth is limited. Repetition in time will result in larger delays and increased power consumption.

Transmitting PDCCH requires, at the base-station (gNB) side, that the DCI payload is transmitted following general steps 1 to 7 below:

Step 1 -Determine Aggregation Level: The gNB determines the AL according to the link adaptation algorithm. In general, UEs in bad coverage get assigned larger ALs than UEs in good coverage conditions.

Step 2 -Generate DCI payload: The gNB generate the DCI according to UE configuration and the control information it wants to transmit.

Step 3 -Attach 24-bit cyclic redundancy check (CRC) : From the DCI payload, a 24-bit CRC is generated and scrambled with the appropriate radio network temporary identifier (RNTI) .

Step 4 -Channel encoding: Polar coding is used to encode the payload and CRC.

Step 5 -Rate matching: From the generated codeword only those bits that fit into the allocated resources are transmitted, taking the demodulation reference signal (DMRS) into account. Also, an interleaving is applied.

Step 6 -PDCCH encoding: The bits from the channel coding are scrambled and mapped to a quadrature phase shift keying (QPSK) symbols. The gNB can apply a transmit diversity scheme and pre-code control data and DMRS.

Step 7 -Resource mapping: The QPSK symbols are mapped onto the control channel elements (CCEs) and resource element groups (REG) according to the CCE-to-REG mapping defined in the CORESET.

At the receiver side, the UE searches for PDCCH candidates in the configured search space sets. In each search space set, the UE configured to search for specific DCIs. For instance, in a UE-specific search space set the UE will look for UL allocations DCI Formats 0_0 or 0_1 or for DL allocations DCI formats 1_0 or 1_1. The UE is also (pre) configured with the payload size of each DCIs. However, when the UE does not have the configuration information for an exact DCI Format, the AL and the associated resources in the CORESET it must blindly try all possible combinations. The necessary steps can be summarized as follows:

Step 1 -Choose a DCI Format: The payload of the DCI is known through pre-configuration.

Step 2 -Choose an AL: The AL defines the number of resources (i.e. CCEs) for the decoding attempt.

Step 3 -Try decoding: For all possible resources allocation for that AL try to decode the PDCCH. The decoding is successful if the CRC is correct, i.e. the CRC corresponds to the target RNTI. If unsuccessful, go back to step 2 and try a different AL.

The above procedure is repeated for every DCI Format with a different payload. If payloads are the same, the DCI Format is differentiated with a flag inside the payload indicating the format.

The apparatus, systems and methods described herein extend the CORESET to a duration of more than 3 symbols by introducing a CORESET extension which directly maps to the resources in the regular CORESET. Therefore, the UE decodes PDCCH candidates utilizing resources in both CORESET and CORESET extension to improve reliability/coverage. This results in reduced decoding delay since the extended CORESET is contiguous, reduced power consumption since the RF can be switched off after successful reception, and reduced memory consumption, because fewer repetitions are buffered and combined before decoding is attempted. Additionally, the number of blind decoding attempts remains the same as previous systems but there is an increased diversity gain, since CORESET and its extension can be configured with different CCE-to-REG mappings.

For instance, a CORESET with 4 symbols can be configured with a CORESET duration of 3 symbols and a 1 symbol extension, a CORESET duration of 2 symbols and 2-symbol extension or a CORESET duration of 1 symbol and a 3-symbol extension. Figure 2 shows an example of a CORESET of 3 symbols with an extension of another 3 symbols. This CORESET is referred to as extended CORESET and the additional symbols are called CORESET extension.

The CORESET extension can also be configured dynamically through a dedicated DCI, which may enable or disable the extension or re-configured it. The extension can span the same frequency resources as the CORESET or different frequency resources.

The CORESET extension is implicitly linked (or mapped) to the PDCCH candidates of the CORESET. This avoids treating the extension together with the CORESET as a normal large CORESET, thereby increasing the PDCCH search space and hence the number of blind decoding attempts, which is undesirable for REDCAP UEs with reduced PDCCH de-coding capabilities.

Not all the resources in the CORESET need to be linked to the CORESET extension. For instance, PDCCH candidates with CCE indices from 0 to 7 are not linked to the CORESET extension, whereas PDCCH candidates with CCE indices from 8 to 15 are linked to the CORESET extension. This would allow the gNB keep a part of the CORESET for UEs with good coverage that do not require large ALs and to focus the additional resources in the extension to UEs with low coverage. An example is shown in Figure 3, where REGs 36 to 53 are not associated with the CORESET extension and REGs 0 to 35 are associated with the CORESET extension. The associated resources can be indicated in terms of REGs, CCEs or physical resources blocks (PRBs) .

The association of resources in the CORESET to resources in the CORESET extension can be configured in various ways. One way is to configure a bit string indicating which resources are associated. In the example in Figure 3, the frequencyDomainResources are configured via bit string 01111111111111111110, where the leftmost zero corresponds to PRBs 0 to 5. The frequencyDomainResources for the associated resources are then given by 01111111111110000000. Equivalently, the non-associated resources can be indicated.

The configuration via a bitmap allows for maximum flexibility but consumes signaling bandwidth. Therefore, a more compact form may be to introduce possible fractions of associated CORESET resources, e.g. 1/2, 3/4, 2/3, 1/3, 1/4 etc. such that, for example, only the first half of the resources in the CORESET are associated to the extension. Additionally, an offset parameter may be introduced to increase flexibility. Again, taking the example in Figure 3, only 2/3 of the CORESET resources are associated with the extension, i.e. 12 out of 18 REGs. The offset parameter is 0 REGs in this example but could be any integer between 0 and 6. For instance, if the offset is 3 REGs then PRBs 24 to 95 would be associated with the extension.

Moreover, to maximize frequency diversity, the CORESET and CORESET extension can be interleaved separately. That can be achieved by using all the interleaving parameters reg-BundleSize, interleaverSize and shiftIndex or just some parameters such as shiftIndex. This will ensure that the resources in the CORESET and the CORESET extension do not occupy the same frequency resources to maximize robustness against frequency selective fading.

UEs that do not support extended CORESETs can still receive control information in the normal CORESET. The resource of the extension can be accounted for and signalled as reserved resources so that those UEs compute the correct amount of resources for data.

To use the additional resources in the CORESET extension for PDCCH transmission, all the resources may be used to encode the PDCCH with the highest possible code rate. All candidate resources in both CORESET and CORESET extension are used to attempt to decode the PDCCH. For instance, a UE tries to decode AL 4 in the CORESET and is preconfigured to recognise the locations of another 4 CCEs in the CORESET extension. Therefore, to attempt to decode the PDCCH candidate it uses all the 8 CCEs which is effectively an AL of 8.

Therefore, the UE will search for PDCCH candidates taking into account the combined resources when determining the AL. For instance, if 1 CCE in the CORESET is associated with 1 CCE in the extension, the UE will not search AL 1, since the smallest AL is 2. That also means that ALs such as 5 or 12 are possible. However, blind decoding attempts will not be increased.

The ratio of CORESET resources to resources in the CORESET extension may also be configurable. This can be achieved for instance by configuring resource that are not associated to the CORESET extension.

Alternatively, the PDCCH may be repeated in the CORESET extension and combined with the PDCCH in the CORESET. Thus, the UE can combine both transmissions and subsequently decode the PDCCH candidate.

The number of repetitions maybe be configurable and given via the mapping of resources between the CORESET and the CORESET extension. For instance, if for

AL

2, 2 CCEs in the CORESET are associated with 4 CCEs in the CORESET extension, then the PDCCH over 2 CCEs is repeated twice in the extension.

The apparatus, systems and methods described herein may use implicit mapping of the resources indicated in the CORESET extension. The CCEs in the CORESET may map to another (possible different) set of CCEs in the CORESET extension. Moreover, the mapping may be fixed and can only be changed semi-statically.

The REGs may be indexed separately for the CORESET and the CORESET extension. Hence, a simple mapping rule is used to associate N CCEs with indexes n = 0, 1, ..., N -1 to N CCEs with the same indices n in the CORESET extension. Figure 4 illustrates an example where 4 CCEs of the CORESET are mapped to the 4 CCEs of the extension, that is where only REGs 0 to 23 are associated with the CORESET extension. In this example, assuming PDCCH encoding across all resource, the UE will start decoding PDCCH candidates with AL 2, i.e. 1 CCE from the CORESET and 1 CCE from the extension resulting in 4 PDCCH candidates. Similarly, the UE decodes AL 4 with PDCCH candidates spanning CCE0/CCE1 and CCE2/CCE3. Finally, one PDCCH candidate with AL 8 spanning all the 8 CCEs.

The CORESET and CORESET extension may have a different CCE-to-REG mapping. Figure 5 illustrates an extended CORESET with 2-symbol extension where CORESET and CORESET extension have a different CCEREG mapping. More precisely, the CORESET has a REG bundle size of 6 whereas the CORESET extension has a REG bundle size of 2. Both have an interleaver depth of 3, i.e. the CORESET bandwidth is divided into 3 sections.

The same mapping rule may apply, that is CCEs 0 to 3 in the CORESET are associated with CCEs 0 to 3 in the CORESET extension. However, due to interleaving they correspond to different REGs.

There may be configurations where the number of resources in the CORESET and the CORESET extension are different. Consider the example in Figure 6, where 2 CCEs are associated to 4 CCEs in the extension. In this case, 1 CCE in the CORESET is associated with 2 CCEs in the CORESET extension.

For instance, CCE 0 is associated with CCE 0/1 and CCE 1 with CCE 2/3. The general mapping rule can be defined as follows: Denote

and N _CCE,p the number of associated CCEs in the CORESET extension and the CORESET p respectively. If

CCE n in CORESET p, with n=0, 1, …, N _CCE,p is associated toCCE m in the CORESET extension via m=R _CCE,p·n+i (1)

Similarly, if

CCE m in the CORESET extension with m=0, 1, …, N _CCE,p is associated to CCE n in the CORESET p via

n=R _CCE,p·m+i (2)

where

and i=0, …, R _CCE,p-1

When there are less CCEs in the CORESET extension than in the associated CORESET

then multiple CCEs in the CORESET are associated to one CCE in the CORESET extension. Figure 7 shows an extended CORESET with 1-symbol extension where 4 CCEs in the CORESET are associated to 2 CCEs in the CORESET extension. Using this example and according to formula (2) above, CCE0 and CCE1 in the CORESET extension are associated with CCE0/1 and CCE2/3, respectively. For PDCCH candidate decoding this means that the UE will attempt to decode 4 times AL 2, i.e. CCEs 0/ (0) , 1/ (0) , 2/ (1) and 3/ (1) 2, 2 times AL 3, i.e. CCEs 0/1/ (0) and 2/3/ (1) , and once AL 6, i.e. CCEs 0/1/2/3/ (0/1) , where CCEs x/ (y) means CCEs x in the CORESET and CCEs y in the CORESET extension.

Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

The signal processing functionality of the embodiments of the invention especially the gNB and the UE 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. 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 module.

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. 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) (RTM) read or write drive (R or RW) , or other removable or fixed media drive. 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.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card) , a communications port (such as for example, a universal serial bus (USB) port) , a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms ‘computer program product’ , ‘computer-readable medium’a nd 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 45 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.

The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory. 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.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a 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.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices.

Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to ‘a’ , ‘an’ , ‘first’ , ‘second’ , etc. do not preclude a plurality.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term ‘comprising’ or “including” does not exclude the presence of other elements.

Claims

A method of transmitting downlink control information from a base station to a UE in a cellu-lar communications network utilising an OFDM transmission format, the method comprising:

defining a main CORESET comprising a plurality of PDCCH candidates;

defining a CORESET extension comprising a plurality of PDCCH candidates; and

mapping at least one of the plurality of PDCCH candidates in the CORESET extension to at least one of the plurality PDCCH candidates in the main CORESET.
Themethod according to claim 1, wherein the plurality of PDCCH candidates in the CORE-SET extension is mapped to a fraction of the plurality of PDCCH candidates in the main CORESET.
The method according to claim 2, wherein an offset parameter indicates an offset applied to the CORESET extension.
Themethod according to claim 1, wherein the main CORESET and the CORESET exten-sion are interleaved before transmission.
The method according to any preceding claim, wherein the mapping step uses a configur-able mapping or an implicit mapping.
The method according to any preceding claim wherein a PDCCH candidate is encoded and mapped onto a CCE, and wherein the UE uses at least one CCE in the main CORESET and at least one CCE in CORESET extension to decode a PDCCH candidate.
The method according to any of claims 1 to 6 wherein the method further comprises:

determining an aggregation level and assigning the aggregation level to the UE;

generating a DCI payload;

attaching a CRC to the DCI payload;

encoding the DCI payload and CRC to generate a codeword;

rate matching the codeword to produce a channel coding using the demodulation reference signal;

scrambling and mapping the channel coding to a plurality of QPSK symbols;

mapping the QPSK symbols to at least one CCE and at least one REG, using a mapping scheme defined in the main CORESET; and

using the at least one CCE and the at least one REG in the main CORESET.
The method according to claim 7 wherein the at least one REG in the main CORESET is indexed independently from a second at least one REG used in the CORESET extension.
A base station configured to perform the method of any preceding claim.
A UE configured to decode the main CORESETand the CORESET extension of any of claims 1 to 8.