WO2022017399A1

WO2022017399A1 - Search space bundling

Info

Publication number: WO2022017399A1
Application number: PCT/CN2021/107462
Authority: WO
Inventors: Hongzhi Wang; Umer Salim; Sebastian Wagner
Original assignee: Huizhou Tcl Cloud Internet Corporation Technology Co., Ltd.
Priority date: 2020-07-23
Filing date: 2021-07-20
Publication date: 2022-01-27
Also published as: CN116326079A

Abstract

Methods for bundling search spaces for the transmission of downlink control channels in an OFDM transmission systems. Search spaces in different monitoring occasions, or different CORESETs, may be bundled to enable repetition of downlink control channels. This enables efficient transmission of downlink control channels without blocking CORESETs.

Description

Search Space Bundling

Technical Field

The following disclosure relates to bundling of search spaces for PDCCH transmission, in particular for reduced-capability 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 ^-6has 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 provide a method of transmitting downlink control information in a cellular communications network utilising an OFDM transmission format, the method comprising defining a bundle of search spaces for transmission of a downlink control channel, wherein the bundle includes control channel elements in at least two monitoring occasions; and transmitting a downlink control channel in control channel elements of a first of the at least two monitoring occasions, and transmitting a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two monitoring occasions.

The transmission in the first monitoring occasion may use a different aggregation level to the transmission in the second monitoring occasion.

The repetition may repeat systematic bits of the downlink control channel and may include different parity bits than the first transmission.

The control channel elements of the first and second monitoring occasions may be in the same CORESET.

The bundle of search spaces may comprise at least one search space set in the CORESET in each monitoring occasion.

The method further may further comprise the step of transmitting an indication of an association between the at least two search spaces.

The indication may permit the UE to decode the repetition without blind decoding.

The bundle of search spaces may comprise a single search space set in each monitoring occasion.

The control channel elements of the first and second monitoring occasions may be in different CORESETS.

The repetition may include a subset of the bits transmitted in the first transmission, the method may further comprise transmitting a second repetition of at least part of the downlink control channel, wherein the second repetition may include a different subset than the subset transmitted in the first repetition.

The location of the control channel elements of the second monitoring occasion may be related to the location of the control channel elements of the first monitoring occasion.

The method may further comprise transmitting information regarding the bundle of search spaces.

The information may include an indication of how the location of the control channel elements of the second monitoring occasion are related to the location of the control channel elements of the first monitoring occasion.

The information may include the identity of CORESETs which are bundled.

The bundle of CORESETs may be identified by a specific CORESET ID.

The specific CORESET ID may be defined based on the CORESET IDs of CORESETs which are included in the bundle.

The systematic bits may be bits representing a DCI message and the CRC.

The CCE index of control channel elements used in the second monitoring occasion may be defined by a function of the CCE index of the control channel elements used in the first monitoring occasion.

The function may be: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels)

There is also provided a method of transmitting downlink control information in a cellular communications network utilising an OFDM transmission format, the method comprising defining a bundle of search spaces for transmission of a downlink control channel, wherein the bundle includes control channel elements in at least two CORESETs in a single monitoring occasion; and transmitting a downlink control channel in control channel elements of a first of the at least two CORESETs, and transmitting a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two CORESETs.

The transmission in the first CORESET may use a different aggregation level to the transmission in the second CORESET.

The repetition may repeat systematic bits of the downlink control channel and includes different parity bits than the first transmission.

The location of the control channel elements of the second CORESET may be related to the location of the control channel elements of the first CORESET.

The information may include an indication of how the location of the control channel elements of the second CORESET are related to the location of the control channel elements of the first CORESET.

The information may include the identity of CORESETs which are bundled.

The bundle of CORESETs may be identified by a specific CORESET ID.

The systematic bits may be bits representing a DCI message and the CRC.

The CCE index of control channel elements used in the second CORESET may be defined by a function of the CCE index of the control channel elements used in the first CORESET.

The function may be: -

There is also provided a method performed at a UE in a cellular communications network utilising an OFDM transmission format, the method comprising defining a bundle of search spaces for receiving a downlink control channel, wherein the bundle includes control channel elements in at least two monitoring occasions; and receiving a downlink control channel in control channel elements of a first of the at least two monitoring occasions, and receiving a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two monitoring occasions.

The received transmission in the first monitoring occasion may use a different aggregation level to the transmission received in the second monitoring occasion.

The method may further comprise the step of transmitting an indication of an association between the at least two search spaces.

The repetition may include a subset of the bits transmitted in the first transmission, the method further comprising receiving a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.

The location of the control channel elements of the second monitoring occasion is related to the location of the control channel elements of the first monitoring occasion.

The method may further comprise receiving information regarding the bundle of search spaces.

The information may include the identity of CORESETs which are bundled.

The bundle of CORESETs may be identified by a specific CORESET ID.

The systematic bits may be bits representing a DCI message and the CRC.

The function may be: -

The UE may decode the first transmission blindly, and may decode the second transmission based on a received indication.

There is also provide a method performed at a UE in a cellular communications network utilising an OFDM transmission format, the method comprising defining a bundle of search spaces for receiving a downlink control channel, wherein the bundle includes control channel elements in at least two CORESETs in a single monitoring occasion; and receiving a downlink control channel in control channel elements of a first of the at least two CORESETs, and receiving a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two CORESETs.

The transmission received in the first CORESET may use a different aggregation level to the transmission received in the second CORESET.

The repetition may includes a subset of the bits transmitted in the first transmission, the method further comprising receiving a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.

The information may include the identity of CORESETs which are bundled.

The bundle of CORESETs may be identified by a specific CORESET ID.

The systematic bits may be bits representing a DCI message and the CRC.

The function may be: -

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

There is also provided a UE configured to perform the methods described herein.

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 a schematic diagram of selected elements of a cellular communications network;

Figure 2 shows an example of bundling over two occasions of one CORESET;

Figure 3 shows an example bundling over one occasion of two CORESETs;

Figure 4 shows an example of forming repetitions of a PDCCH;

Figure 5 shows an example of soft-combining;

Figure 6 shows an example of forming a PDCCH signal; and

Figure 7 shows a further example of soft-combining.

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.

Reduced Capability (REDCAP) devices are proposed for use in NR for use cases which require more functionality than LPWA (LTE-M/NB-IoT) , but less than URLLC/eMBB services. Cost reduction is a primary driver, but improved battery life and reduced size are also attractive. One aspect of the proposal for REDCAP devices is a reduced number of antennas, and a reduction in device bandwidth, which may lead to a reduction in coverage for REDCAP devices.

Due to the reduction of number of UE RX antennas and bandwidth, it is expected that the downlink coverage will be impacted. Simulation results in R1-2003303 show there is nearly 3 dB performance loss for aggregation level 16 when RX antennas are reduced from 4RX to 2RX and around 6 dB loss for a reduction from 4RX to 1 RX. A particular concern due to this reduction in performance is the reliability of PDCCH which due to the reduced bandwidth for REDCAP may not be able to use the highest aggregation levels. Disclosed below are methods and techniques which aim to compensate for the reduced coverage for PDCCH for reduced capability devices but may also be applicable to devices and systems.

The following terminology is utilised in this disclosure. The disclosure is principally directed to the NR standards, but is also applicable to the LTE standards.

● A resource block (RB) is the smallest unit of time/frequency resources that can be allocated to a user. The resource block is x-KHz wide in frequency and 1 slot long in time. The number of subcarriers used per resource block for PDCCH is 12 and the exact value x depends on the subcarrier spacing (x=12*SCS) which can be 15 KHz, 30 KHz, 60 KHz, etc. In terms of time, the default slot duration in NR is 14 OFDM symbols but there is also mini-slot duration possible (e.g. 1, 2, 4, 7, etc. OFDM symbols) . The exact time duration of a slot in milliseconds (ms) depends on the number of OFDM symbols in this given slot and on SCS, e.g. for 15 KHz SCS and 14 OFDM symbols, 1 slot is 1 ms long.

● A resource-element group (REG) equals one RB during one OFDM symbol.

● A control-channel element (CCE) consists of 6REGs.

● The physical downlink control channel (PDCCH) is a physical channel that carries downlink control information (DCI) . A PDCCH consists of one or more CCEs (e.g. L∈ {1, 2, 4, 8} ) . This number is defined as the CCE aggregation level (AL) . For PDCCH blind decoding, the set of ALs and the number of PDCCH candidates per CCE AL per DCI format size that the UE monitors can be configured.

● For each serving cell, a UE is configured with a number of control resource sets (CORESETs) to monitor PDCCH. Each CORESET is defined by: starting OFDM symbol, time duration (consecutive symbols, up to 3) , set of RBs, CCE-to-REG mapping (and REG bundle size in case of interleaved mapping) .

● CCEs can be mapped on the REGs in the CORESET in a localized or distributed manner. The distributed resource mapping is realized by interleaving and the interleaving is operated on the REG bundles. In case of non-interleaved CCE-to-REG mapping, B=6. In case of interleaved CCE-to-REG mapping, B∈ {2, 6} for 1 or 2 symbol CORESET, B∈ {3, 6} for 3 symbol CORESET.

● A PDCCH search space at CCE AL L is defined by a set of PDCCH candidates for this CCE AL.

● We define the PDCCH blocking as the event when the base station (or the network) does not have enough in the control region (or CORESET) of a cell so that at least one user in this cell does not get assigned these control resources and is not scheduled in the current transmission occasion even though it needed service in this occasion. PDCCH blocking probability is the probability with which this event happens.

In order to enhance coverage of PDCCH search space bundling techniques are disclosed below. The techniques are intended to provide improved flexibility for PDCCH scheduling than using higher aggregation levels, while staying within the practical limits for decoding PDCCH, particularly considering the target of the techniques is devices with reduced capability. The intention of the following disclosure is to achieve similar performance as higher aggregation levels without consuming more resources. In a first technique search space bundling may be implemented for different monitoring occasions of the same CORESETs, while in a second technique search space bundling is used in the same or different monitoring occasions but with different CORESETs.

In general PDCCH transmission with higher aggregation levels consumes a large amount of resources and blocking is a significant issue as the network may not have sufficient resources in the control region for further UEs in the same monitoring occasion, which is exacerbated for REDCAP devices with reduced bandwidth. In a first example, PDCCH repetition is performed in a set of bundled search spaces, the search spaces being in different monitoring occasions, but in the same CORESET as shown in Figure 2. The aggregation level of each search space is less than the aggregation level that would be required if only transmitting within one search space, but comparable reliability may be achieved due to the repetition in time between monitoring occasions. This technique reduces the resources required in each monitoring occasion due to the lower aggregation level. However, decoding latency is increased.

The bundling of search spaces for PDCCH repetition may be pre-configured for relevant UEs, for example using higher layer (RRC) signalling.

Utilising different aggregation levels in each monitoring occasion may also provide increased flexibility by selecting specific combinations, and may enable additional aggregation levels. For example, the network may configure one transmission at aggregation level 4 and one at aggregation level 8 in two consecutive monitoring occasions of a CORESET, which is expected to provide equivalent performance to one transmission at aggregation level 12.

Soft combining may be utilised to achieve benefits from the time repetition of PDCCH, but will increase the complexity and blind decoding of the decoding operation if repetition information is not provided in advance since the UE must blind-decode all possible bundles. Sharing the configuration of the bundle with the UE in advance reduces the blind-decoding complexity.

In the example of Figure 2 one candidate in the first search space is associated with one candidate in the second search space. Search Space 1 is configured with candidates at aggregation levels 1 and 2 (AL 1 and 2) , and search space 2 is configured with candidates at aggregation levels 2 and 4 (AL2 and 4) . This configuration may be performed using the parameter nrofCandidates in the searchSpace configuration. In Figure 2 the candidate in the first search space has AL 2 (CCE index 0) , and that in the second search space has AL4 (CCE index 4) . The particular candidates and configuration are given for example only to demonstrate the principle of a defined mapping between candidates in different search spaces for repetition of PDCCH in time.

The repetition of PDCCH in the same CORESET may be configured using one of the following methods.

First, two different search space sets are configured over one CORESET for PDCCH repetition and their association is indicated to the UE. The association allows the UE to decode the repetitions without requiring blind decoding.

A single search space set is configured and the PDCCH is repeated over different instances of the same search space set. The PDCCH configuration indicates to the UE which blind decodes it will perform to decode the PDCCH jointly from the two instances of the search space.

The PDCCH configuration via information element PDCCH-config includes the information about the search space bundling and is signalled to the UE. The bundling information includes: -

● Which search space sets are bundled (there can be multiple bundles) . In a bundle, only a single search space can be indicated, in which case PDCCH repetition is carried out across PDCCH candidates of a single search space set

● Information on how the PDCCH is transmitted in the bundled search space (e.g. repetition scheme)

Special search spaces can be defined which may be used only for PDCCH repetition. As an example, a search space 1, SS1, may be configured to have PDCCH with or without repetition. It could be bundled with an SS2, which is only configured for bundling purposes. Thus, only a PDCCH which has been transmitted over SS1 may be repeated over SS2. To achieve this flexibility of PDCCH repetition without exponential complexity, SS2 can be configured with limited number of suitable PDCCH candidates which a configured UE will use for joint decoding of repeated PDCCH.

In an alternative configuration searches spaces in different CORESETs may be bundled for PDCCH repetition, as shown in Figure 3. In a similar configuration to the previous arrangement, different aggregation levels can be utilised for each repetition in the different CORESETs.

A new CORESET ID may be utilised to indicate the CORESETs being utilised. For example, a temporary CORESET ID can be defined as follows when using two CORESETs in one BWP: -

new CORESET ID = 3*CORESET ID 1 +CORESET ID 2

The new CORESET ID is transmitted by the network to the UE using RRC signalling. At the UE the two CORESET IDs can be calculated using the modulo function. A new search space ID can also be created using the same method. The search space list and CORESET list are included in the information element PDCCH-config. So that the new CORESET ID or search space ID can be used as indication of the bundled CORESETs or the bundled search spaces among the list.

In the example of Figure 3 PDCCH is repeated in different CORESETs in the same monitoring occasion. The repetition is therefore in the frequency domain in this example. The same principles apply to the use of different CORESETs in different monitoring occasions. The search spaces of different CORESETs may be bundled for PDCCH repetitions of the same DCI content. Thus, an additional diversity gain may be obtained due to repetition in the different CORESETs since the different CORESETs are located on different frequency bands. The configuration of the PDCCH repetition can be set by two methods explained above.

The PDCCH messages to be transmitted in the repetitions may be defined as described in the following disclosure. The systematic bits (that is, the bits representing the message information and the related CRC bits) are transmitted in each repetition with a different set of parity bits, with some additional redundant bits transmitted in each repetition.

The different redundancy versions for each repetition are generated by puncturing the channel coded bits of the systematic bits. Each repetition has a different set of coded bits than the previous repetition; the systematic bits are transmitted in each repetition but the parity bits are different for each repetition. At the receiver each received repetition can be stored in a buffer and combined with the later repetitions to improve decoding. The effect of this approach is that the code rate decreases as each repetition is received. Each redundancy version with a high code rate should be part of the low rate mother code.

Figure 4 illustrates an example of PDCCH repetition constructed with the systematic bits and different set of parity bits (P1, P2 and P3) as discussed above. The systematic bits are consist of the DCI message and the CRC for the DCI message. Each repetition can be decoded in isolation as they all include the full set of systematic bits and have some parity bits to assist in decoding. However, by combining repetitions the code rate is reduced and the decoding ability increased.

Figure 5 shows an example in which three repetitions of PDCCH are transmitted in three different monitoring occasions of CORESET 1 (i.e. each repetition in the same CORESET) . As explained in relation to Figure 4, each repetition consists of the systematic bits and a different set of parity bits After the first monitoring occasion 1 the UE attempts to blind decode the PDCCH. If the PDCCH in monitoring occasion 2 also cannot be blind-decoded the UE performs soft combining of the first two repetitions to lower the code rate (due to the different parity bits in the two repetitions) and improve the prospects of decoding PDCCH. If decoding is still unsuccessful the third repetition is available for blind decoding or soft combing with the first two repetitions.

In an alternative arrangement the systematic bits are only transmitted in the initial transmission of PDCCH, and the parity bits are transmitted in all of the repetitions.

The systematic bits of the PDCCH are the DCI and CRC parts of the message which may be encoded with a higher aggregation level (i.e. lower code rate) than each individual repetition. The coded bitsare then punctured into different parts according the number of repetitions to be transmitted with a lower aggregation level than would be used for a single transmission. The systematic and first part of the coded bits are transmitted in the initial transmission with a lower aggregation level, and the remaining coded bits are transmitted in other bundled search spaces which may be located in the same or different monitoring occasions of the same or different CORESETs. Effectively a larger search space with larger aggregation level is constructed from subsets of search spaces with lower aggregation levels.

For example, the systematic bits could be encoded with aggregation level L as shown in Figure 6. The coded bits are splitinto two parts each with aggregation level of L/2 when two repetitions are configured for this PDCCH. The first part is transmitted in the initial transmission and the second part is transmitted in another occasion of the PDCCH transmission. In this approach, only the first transmission is self-decodable since the systematic bits are not repeated in the second transmission. However, the additional parity bits in the subsequent transmission can be utilised to assist decoding.

Figure 7 shows an example in which two repetitions are transmitted in two different monitoring occasions of two different CORESETs (CORESET1 and CORESET2) . The signals transmitted in each repetition may be defined according to the principles described herein. The UE performs a blind detection on the first PDCCH transmission in monitoring occasion 1 of CORESET1. If the first transmission part of the PDCCH is not decoded, the UE will attempt to find the second part of the PDCCH transmission which is located in the monitoring occasion 2 of CORESET2. The indication of two bundling search spaces can be configured using a static predefined pattern function or semi-static configuration, as explained below. The UE can then perform a soft combination with the first part to obtain a PDCCH transmission with higher aggregation level.

The advantage of this arrangement is that the systematic bits are transmitted only once compared with the previous proposals which have the systematic bits in each repetition. Hence the PDCCH repetition with the search space aggregation could get additional coding rate gain because of more parity bits transmitted in the repetitions. Thus the reliability is increased and this will enhance the coverage. The type of soft combing can be defined in the configuration of PDCCH repetition which will be discussed below.

The CCE index of bundled search spaces for repetitions of PDCCH can be defined by a function of the CCE index of the initial PDCCH transmission, CORESET size, repetition number and aggregation levels of associated search spaces.

The parameters of the bundled CORESET sizes, the aggregation levels of bundled search spaces and the repetition number may be set by RRC signalling. The UE performs a blind decoding for the first PDCCH transmission and the CCE index of that initial transmission is obtained by a hash function (for example, as defined in TS38.213) . The candidates of the following retransmissions will be associated with the first candidate. Therefore, a function can be defined to calculate the CCE index of bundling search space as: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels) (1)

As described above, two particular arrangements for bundling search spaces have been disclosed herein:

i. Two different search space sets are configured over the same CORESET and their association for the purpose of PDCCH repetition is indicated to UE.

ii. A single search space set is configured and the PDCCH is repeated over different instances of the same search space set. The PDCCH configuration indicates to UE which blind decodes it will perform to decode the PDCCH jointly from the two instances of the search space.

The second scheme where the PDCCH repetitions are performed over different CORESETs will necessarily need two search spaces, as each search space is associated to a single, different, CORESET.

The PDCCH-config message transmitted to a UE as part of the PDCCH configuration indicates the use of PDCCH repetition, for example by including a flag. The PDCCH configuration also indicates whether the repetitions will be transmitted over a single search space, or two different search spaces. The PDCCH configuration may indicate the identities of the search space (s) that will be utilised.

The configuration of each search space may include the bundling information. A flag can indicate whether a configured search space may have repetitions of PDCCH. When a search space is bundled with a different search space, search spaces can have an indication as to which search space this will be bundled for PDCCH repetitions. This can be achieved by indicating a field as part of search space configuration which provides the identity of the other search space.

Generalizing the configuration to additional search spaces, and providing additional flexibility, the configuration of bundling search spaces over different occasions for the PDCCH repetitions could be indicated by the following two methods. These can be applied with minor adaptations to the three schemes proposed above.

In a first method, the pattern for a set of bundled search spaces with different aggregation level for PDCCH repetition can be predefined by the network and can be provided to the UE through RRC signalling.

The bundled search spaces can be configured with RRC signalling including the aggregation level, number of repetition, resource size, and monitoring occasion positions. Only one configuration of bundled search spaces is pre-defined for PDCCH repetitions. Then this configuration will be applied periodically for the PDCCH repetitions. The parameters of configuration for each search space cannot be changed dynamically during the transmission.

The CCE index of the candidate in the bundled search space can be associated with the candidate in the initial search space. It can be calculated by the function (1) defined above. Below an example mapping function which bundles the search spaces is provided. The function of CCE index calculation for the bundling candidate can be defined as: -

CCE index _bundling = { (CCE index _initial/L _initial +CCE_offset) mod (S _bundling/L _bundling) } * (L _bundling) (2)

Where

S _bundling is the bundling search space size in term of number of CCEs,

CCE_offset ∈ {0, 1, .., min ( (S _initial/L _initial) , (S _bundling/L _bundling) ) -1} ,

L _bundling is the aggregation level of the bundling search space,

L _initial is the aggregation level of the initial search space,

CCE index _initial is calculated using the hash function (2) defined in TS38.213.

The parameters CCE_offset, L _initial, L _bundling and S _bundling can be configured by RRC signalling. The CCE index _initial can be obtained with hash function (3) for the first blind decoding. Then the CCE index _bundling can be calculated with the function (2) for the following associated candidates in the bundled search space. The parameter CCE_offset gives more flexibility for the resource allocation of PDCCH transmission in the search space bundling.

In a second method multiple configurations of search space bundle based PDCCH repetitions can be configured by RRC signalling. The network can restrict the number of active configurations in order to reduce blind decoding requirements at the UE. The configurations ID can also be associated with different sequences of PDCCH DMRS. In this case, only one configuration is enabled for each PDCCH transmission, but it can be updated dynamically from one transmission to another by changing the sequences of PDCCH DMRS.

The aggregation level, search space size, the CCE index for each bundling search space and the soft combining type could be configured by RRC signalling. The blind decoding requirements increase when PDCCH repetition is configured. It can result in the highest number of blind decoding if all choices of combinations are used. Hence, the number of combinations should be limited. One solution is that the network can schedule certain pre-defined configurations of the combination with different aggregation level in search spaces. Hence, there is still certain number of blind decoding due to the combination, but the complexity is limited.

Another solution is that only one configuration can be dynamically enabled during each PDCCH transmission. Different sequences of PDCCH DMRS are associated to different bundling configurations. Thus, the configuration ID can be identified by performing the correlation function of different sequences of PDCCH DMRS. Compared to predefined pattern used in the proposal 2, this method provides more flexibility to the network in terms of resources management. The network can schedule the PDCCH repetitions with different combinations in function of the current available resources in the search spaces.

For example, the network schedules one PDDCH initial transmission and two repetitions with the combination of different aggregation levels (AL 4, AL 8 and AL 16) . Four possible configurations are listed in the table 1. The network could employ the

configuration

2 or 3 if the search space for AL 8 is available in the first monitoring occasion. It will use configuration 2 if it deems suitable to stay with AL 4 and AL 8. If the channel conditions are poor, and the network decides to employ AL 8 and AL 16, it may use configuration 3. Otherwise, the configuration 0 or 1 could be scheduled for the initial transmission depending upon the available resources for each PDCCH repetition. Some combination gains are obtained through time domain repetition.

Therefore, it can enhance the coverage.

Table 1

In such schemes, the DMRS will indicate the configuration index, thus UE will know which configuration is active. Then it can use the known configuration of bundled search spaces to perform joint decoding over the PDCCH repetitions of the active configuration.

In summary of the above disclosure PDCCH repetitions can be performed over different CORESETs with bundled search spaces in different aggregation level for coverage enhancement. The CCE index of the bundled search space is associated with the CCE index of initial search space. The approach is more flexible in term of PDCCH scheduling with different methods of configuration. The different PDCCH repetition methods provide more flexibility for resources management and reduce the probability of blocking issue.

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’ 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 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 in a cellular communications network utilising an OFDM transmission format, the method comprising

defining a bundle of search spaces for transmission of a downlink control channel, wherein the bundle includes control channel elements in at least two monitoring occasions; and

transmitting a downlink control channel in control channel elements of a first of the at least two monitoring occasions, and transmitting a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two monitoring occasions.
The method according to claim 1, wherein the transmission in the first monitoring occasion uses a different aggregation level to the transmission in the second monitoring occasion.
The method according to claim 1 or claim 2, wherein the repetition repeats systematic bits of the downlink control channel and includes different parity bits than the first transmission.
The method according to any preceding claim, wherein the control channel elements of the first and second monitoring occasions are in the same CORESET.
The method according to claim 4, wherein the bundle of search spaces comprises at least one search space set in the CORESET in each monitoring occasion.
The method according to claim 5, wherein the method further comprising the step of transmitting an indication of an association between the at least two search spaces.
The method according to claim 6, wherein the indication permits the UE to decode the repetition without blind decoding.
The method according to claim 1, wherein the bundle of search spaces comprises a single search space set in each monitoring occasion.
The method of any of claims 1 to 3, wherein control channel elements of the first and second monitoring occasions are in different CORESETS.
The method according to any preceding claim, wherein the repetition includes a subset of the bits transmitted in the first transmission, the method further comprising transmitting a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.
The method according to any preceding claim, wherein thelocation of the control channel elements of the second monitoring occasion is related to the location of the control channel elements of the first monitoring occasion.
The method according to any preceding claim, further comprising transmitting information regarding the bundle of search spaces.
The method according to claim 12, wherein the information includes an indication of how the location of the control channel elements of the second monitoring occasion are related to the location of the control channel elements of the first monitoring occasion.
The method according to claim 12, wherein the information includes the identity of CORESETs comprising the control channel elements which are bundled.
The method according to claim14, wherein the CORESETs are identified by a specific CORESET ID.
The method according to claim 15, wherein the specific CORESET ID is defined based on the CORESET IDs of CORESETs which are included in the bundle.
A method according to claim 3, wherein the systematic bits are bits representing a DCI message and the CRC.
The method according to any preceding claim, wherein the CCE index of control channel elements used in the second monitoring occasion are defined by a function of the CCE index of the control channel elements used in the first monitoring occasion.
The method according to claim 18, wherein the function is: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels)
A method of transmitting downlink control information in a cellular communications network utilising an OFDM transmission format, the method comprising

defining a bundle of search spaces for transmission of a downlink control channel, wherein the bundle includes control channel elements in at least two CORESETs in a single monitoring occasion; and

transmitting a downlink control channel in control channel elements of a first of the at least two CORESETs, and transmitting a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two CORESETs.
The method according to claim 20, wherein thetransmission in the first CORESET uses a different aggregation level to the transmission in the second CORESET.
The method according to claim 20 or claim 21, wherein the repetition repeats systematic bits of the downlink control channel and includes different parity bits than the first transmission.
The method according to any of claims 20 to 22 preceding claim, wherein the repetition includes a subset of the bits transmitted in the first transmission, the method further comprising transmitting a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.
The method according to any of claims 20 to 23, wherein the location of the control channel elements of the second CORESET is related to the location of the control channel elements of the first CORESET.
The method according to any of claims 20 to 24, further comprising transmitting information regarding the bundle of search spaces.
The method according to claim 25, wherein the information includes an indication of how the location of the control channel elements of the second CORESET are related to the location of the control channel elements of the first CORESET.
The method according to claim 25 or claim 26, wherein the information includes the identity of CORESETs which are bundled.
The method according to claim 27, wherein thebundle of CORESETs is identified by a specific CORESET ID.
The method according to claim 28, wherein the specific CORESET ID is defined based on the CORESET IDs of CORESETs which are included in the bundle.
The method according to claim 22, wherein the systematic bits are bits representing a DCI message and the CRC.
The method according to any of claims 16 to 20, wherein the CCE index of control channel elements used in the second CORESET are defined by a function of the CCE index of the control channel elements used in the first CORESET.
The method according to claim 31, wherein the function is: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels)
A method performed at a UE in a cellular communications network utilising an OFDM transmission format, the method comprising

defining a bundle of search spaces for receiving a downlink control channel, wherein the bundle includes control channel elements in at least two monitoring occasions; and

receiving a downlink control channel in control channel elements of a first of the at least two monitoring occasions, and receiving a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two monitoring occasions.
The method according to claim 33, wherein the received transmission in the first monitoring occasion uses a different aggregation level to the transmission received in the second monitoring occasion.
The method according to claim 33 or claim 34, wherein the repetition repeats systematic bits of the downlink control channel and includes different parity bits than the first transmission.
The method according to any of claims 33 to 35, wherein the control channel elements of the first and second monitoring occasions are in the same CORESET.
The method according to claim 36, wherein the bundle of search spaces comprises at least one search space set in the CORESET in each monitoring occasion.
The method according to claim 37, wherein the method further comprising the step of transmitting an indication of an association between the at least two search spaces.
The method according to claim 38, wherein the indication permits the UE to decode the repetition without blind decoding.
The method according to claim 33, wherein the bundle of search spaces comprises a single search space set in each monitoring occasion.
The method according to any of claims 33 to 36, wherein the control channel elements of the first and second monitoring occasions are in different CORESETS.
The method according to any of claims 33 to 41, wherein the repetition includes a subset of the bits transmitted in the first transmission, the method further comprising receiving a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.
The method according to any of claims 33 to 42, wherein the location of the control channel elements of the second monitoring occasion is related to the location of the control channel elements of the first monitoring occasion.
The method according to any of claims 33 to 43, further comprising receiving information regarding the bundle of search spaces.
The method of claim 44, wherein the information includes an indication of how the location of the control channel elements of the second monitoring occasion are related to the location of the control channel elements of the first monitoring occasion.
The method of claim 44 or claim 45, wherein theinformation includes the identity of CORESETs comprising the control channel elements which are bundled.
The method of claim 46, wherein the bundle of CORESETs is identified by a specific CORESET ID.
The method according to claim 47, wherein the specific CORESET ID is defined based on the CORESET IDs of CORESETs which are included in the bundle.
The method of claim 35, wherein the systematic bits are bits representing a DCI message and the CRC.
The method according to any of claims 33 to 49, wherein the CCE index of control channel elements used in the second monitoring occasion are defined by a function of the CCE index of the control channel elements used in the first monitoring occasion.
The method of claim 50, wherein the function is: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels)
The method according to any of claims 33 to 51, wherein the UE decodes the first transmission blindly, and decodes the second transmission based on a received indication.
A method performed at a UE in a cellular communications network utilising an OFDM transmission format, the method comprising

defining a bundle of search spaces for receiving a downlink control channel, wherein the bundle includes control channel elements in at least two CORESETs in a single monitoring occasion; and

receiving a downlink control channel in control channel elements of a first of the at least two CORESETs, and receiving a repetition of at least part of the downlink control channel in control channel elements of a second of the at least two CORESETs.
The method of claim 53, wherein the transmission received in the first CORESET uses a different aggregation level to the transmission received in the second CORESET.
The method according to claim 53 or claim 54, wherein the repetition repeats systematic bits of the downlink control channel and includes different parity bits than the first transmission.
The method according to any of claims 53 to 55, wherein the repetition includes a subset of the bits transmitted in the first transmission, the method further comprising receiving a second repetition of at least part of the downlink control channel, wherein the second repetition includes a different subset than the subset transmitted in the first repetition.
The method according to any of claims 53 to 56, wherein the location of the control channel elements of the second CORESET is related to the location of the control channel elements of the first CORESET.
The method according to any of claims 53 to 57, further comprising receiving information regarding the bundle of search spaces.
The method according to claim 58, wherein the information includes an indication of how the location of the control channel elements of the second CORESET are related to the location of the control channel elements of the first CORESET.
The method of claim 58 or claim 59, wherein the information includes the identity of CORESETs which are bundled.
The method of claim 60, wherein the bundle of CORESETs is identified by a specific CORESET ID.
The method of claim 61, wherein the specific CORESET ID is defined based on the CORESET IDs of CORESETs which are included in the bundle.
The method of claim 55, wherein the systematic bits are bits representing a DCI message and the CRC.
A method according to any of claims 53 to 63, wherein the CCE index of control channel elements used in the second CORESET are defined by a function of the CCE index of the control channel elements used in the first CORESET.
The method of claim 64, wherein the function is: -

CCE index _bundling = f (CCE index _initial, CORESET size, repetition number, aggregation levels)
A method according to any of claims 53 to 65, wherein the UE decodes the first transmission blindly, and decodes the second transmission based on a received indication.
A base station configured to perform the method of any of claims 1 to 32.
A UE configured to perform the method of any of claims 33 to 66.