Title METHOD, SYSTEM AND APPARATUS

Field

The present application relates to a method, apparatus, system and computer program and in particular but not exclusively to HARQ processes for a user connected to multiple cells in 5G communication systems.

Background A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and/or other nodes by providing carriers between the various entities involved in the communications path. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet. In a wireless communication system at least a part of a communication session between at least two stations occurs over a wireless link. Examples of wireless systems comprise public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). The wireless systems can typically be divided into cells, and are therefore often referred to as cellular systems.

A user can access the communication system by means of an appropriate communication device or terminal. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. The communication device may access a carrier provided by a station, for example a base station of a cell, and transmit and/or receive communications on the carrier. The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. An example of attempts to solve the problems associated with the increased demands for capacity is an architecture that is known as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The LTE is being standardized by the 3rd Generation Partnership Project (3GPP). The various development stages of the 3GPP LTE specifications are referred to as releases. Certain releases of 3GPP LTE (e.g., LTE Rel-1 1 , LTE Rel-12, LTE Rel-13) are targeted towards LTE-Advanced (LTE- A). LTE-A is directed towards extending and optimising the 3GPP LTE radio access technologies. Another proposed communication system is a 5G network Summary

In a first aspect, there is provided a method comprising providing a plurality of automatic repeat request processes associated with a user device and at least two cells associated with the user device, determining an automatic repeat request process, from the plurality of automatic repeat request processes and causing a transmission to the user device using the determined automatic repeat request process.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process.

Determining the automatic repeat request process may comprise selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes.

The method may comprise determining a plurality of subsets of the plurality of automatic repeat request processes, each subset associated with a respective one of the at least two cells. The subsets may be determined semi-statically. The number of automatic repeat request processes in each subset may be determined in dependence on at least one of transport block size and round trip time.

Determining the automatic repeat request process for a cell may comprise selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the cell.

The method may comprise providing information to at least one second cell of the at least two cells, for use in determining the number of automatic repeat request processes in a subset.

The at least two cells may comprise at least one primary cell and at least one secondary cell. The at least two cells may comprise cells using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated. The transmission may comprise the transmission of a packet.

The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services.

In a second aspect, there is provided a method comprising receiving, at a user device associated with at least two cells, a transmission from a first cell associated with the user device using an automatic repeat request process, the automatic repeat request process comprising an automatic repeat request process determined from a plurality of automatic repeat request processes associated with the user device and with the at least two cells.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes.

A plurality of subsets of the automatic repeat request processes may be determined, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically.

The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the first cell.

The number of hybrid automatic repeat request processes in the first subset may be determined in dependence on at least one of transport block size and round trip time.

The at least two cells may comprise at least one primary cell and at least one secondary cell.

The at least two cells may comprise cell using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet.

The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services. In a third aspect, there is provided an apparatus, said apparatus comprising means for providing a plurality of automatic repeat request processes associated with a user device and at least two cells associated with the user device, means for determining an automatic repeat request process, from the plurality of automatic repeat request processes and means for causing a transmission to the user device using the determined automatic repeat request process. The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process.

Means for determining the automatic repeat request process may comprise means for selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes.

The apparatus may comprise means for determining a plurality of subsets of the plurality of automatic repeat request processes, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically. The number of automatic repeat request processes in each subset may be determined in dependence on at least one of transport block size and round trip time.

Means for determining the automatic repeat request process for a cell may comprise means for selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the cell.

The apparatus may comprise means for providing information to at least one second cell of the at least two cells, for use in determining the number of automatic repeat request processes in a subset.

The at least two cells may comprise at least one primary cell and at least one secondary cell.

The at least two cells may comprise cells using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet. The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services. In a fourth aspect, there is provided an apparatus, said apparatus comprising means for receiving, at a user device associated with at least two cells, a transmission from a first cell associated with the user device using an automatic repeat request process, the automatic repeat request process comprising an automatic repeat request process determined from a plurality of automatic repeat request processes associated with the user device and with the at least two cells.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes. A plurality of subsets of the automatic repeat request processes may be determined, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the first cell. The number of hybrid automatic repeat request processes in the first subset may be determined in dependence on at least one of transport block size and round trip time.

The at least two cells may comprise at least one primary cell and at least one secondary cell. The at least two cells may comprise cell using the same radio access technology or cells using different access technology. The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet. The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services.

In a fifth aspect, there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to provide a plurality of automatic repeat request processes associated with a user device and at least two cells associated with the user device, determine an automatic repeat request process, from the plurality of automatic repeat request processes and cause a transmission to the user device using the determined automatic repeat request process.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. The apparatus may be configured to select an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes.

The apparatus may be configured to determine a plurality of subsets of the plurality of automatic repeat request processes, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically. The number of automatic repeat request processes in each subset may be determined in dependence on at least one of transport block size and round trip time.

The apparatus may be configured to select an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the cell. The apparatus may be configured to provide information to at least one second cell of the at least two cells, for use in determining the number of automatic repeat request processes in a subset. The at least two cells may comprise at least one primary cell and at least one secondary cell.

The at least two cells may comprise cells using the same radio access technology or cells using different access technology. The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet.

The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services.

In a sixth aspect, there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to receive, at a user device associated with at least two cells, a transmission from a first cell associated with the user device using an automatic repeat request process, the automatic repeat request process comprising an automatic repeat request process determined from a plurality of automatic repeat request processes associated with the user device and with the at least two cells.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes. A plurality of subsets of the automatic repeat request processes may be determined, each subset associated with a respective one of the at least two cells. The subsets may be determined semi-statically.

The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the first cell.

The number of hybrid automatic repeat request processes in the first subset may be determined in dependence on at least one of transport block size and round trip time.

The at least two cells may comprise at least one primary cell and at least one secondary cell.

The at least two cells may comprise cell using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet. The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services.

In a seventh aspect there is provided a computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising providing a plurality of automatic repeat request processes associated with a user device and at least two cells associated with the user device, determining an automatic repeat request process, from the plurality of automatic repeat request processes and causing a transmission to the user device using the determined automatic repeat request process.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. Determining the automatic repeat request process may comprise selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes.

The process may comprise determining a plurality of subsets of the plurality of automatic repeat request processes, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically. The number of automatic repeat request processes in each subset may be determined in dependence on at least one of transport block size and round trip time.

Determining the automatic repeat request process for a cell may comprise selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the cell.

The process may comprise providing information to at least one second cell of the at least two cells, for use in determining the number of automatic repeat request processes in a subset.

The at least two cells may comprise at least one primary cell and at least one secondary cell.

The at least two cells may comprise cells using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated.

The transmission may comprise the transmission of a packet.

The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services. In an eighth aspect there is provided a computer program embodied on a non-transitory computer-readable storage medium, the computer program comprising program code for controlling a process to execute a process, the process comprising receiving, at a user device associated with at least two cells, a transmission from a first cell associated with the user device using an automatic repeat request process, the automatic repeat request process comprising an automatic repeat request process determined from a plurality of automatic repeat request processes associated with the user device and with the at least two cells.

The automatic repeat request process may be one of a hybrid automatic repeat request process and a stop and wait process. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes. A plurality of subsets of the automatic repeat request processes may be determined, each subset associated with a respective one of the at least two cells.

The subsets may be determined semi-statically. The determined automatic repeat request process may comprise an automatic repeat request identifier selected from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the first cell. The number of hybrid automatic repeat request processes in the first subset may be determined in dependence on at least one of transport block size and round trip time.

The at least two cells may comprise at least one primary cell and at least one secondary cell. The at least two cells may comprise cell using the same radio access technology or cells using different access technology.

The at least two cells may be co-located or geographically separated. The transmission may comprise the transmission of a packet. The transmission may comprise a transmission of a first service of a plurality of services, wherein the plurality of automatic repeat request processes is useable with each of the plurality of services.

In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above. Description of Figures

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which: Figure 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices;

Figure 2 shows a schematic diagram of an example mobile communication device; Figure 3 shows a schematic diagram of a communication network comprising a UE connected to two different cells , i.e., in communication with a macro eNB and a remote radio head connected to the centralized baseband unit at the macro eNB location by a non- ideal fronthaul link; Figure 4 shows an example method of providing a common pool of HARQ processes for a user device;

Figure 5 shows a schematic diagram of an example pool of HARQ processes for a user device connected to a MeNB and a SeNB;

Figure 6 shows a graph of percentage peak throughput gains of HARQ pooling over HARQ split;

Figure 7 shows a schematic diagram of an example control apparatus; Detailed description Before explaining in detail the examples, certain general principles of a wireless

communication system and mobile communication devices are briefly explained with reference to Figures 1 to 2 to assist in understanding the technology underlying the described examples.

In a wireless communication system 100, such as that shown in figure 1 , mobile

communication devices or user equipment (UE) 102, 104, 105 are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. Base stations are typically controlled by at least one appropriate controller apparatus, so as to enable operation thereof and management of mobile communication devices in communication with the base stations. The controller apparatus may be located in a radio access network (e.g. wireless communication system 100) or in a core network (CN) (not shown) and may be implemented as one central apparatus or its functionality may be distributed over several apparatus. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller. In Figure 1 control apparatus 108 and 109 are shown to control the respective macro level base stations 106 and 107. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

LTE systems may however be considered to have a so-called "flat" architecture, without the provision of RNCs; rather the (e)NB is in communication with a system architecture evolution gateway (SAE-GW) and a mobility management entity (MME), which entities may also be pooled meaning that a plurality of these nodes may serve a plurality (set) of (e)NBs. Each UE is served by only one MME and/or S-GW at a time and the (e)NB keeps track of current association. SAE-GW is a "high-level" user plane core network element in LTE, which may consist of the S-GW and the P-GW (serving gateway and packet data network gateway, respectively). The functionalities of the S-GW and P-GW are separated and they are not required to be co-located.

In Figure 1 base stations 106 and 107 are shown as connected to a wider communications network 113 via gateway 1 12. A further gateway function may be provided to connect to another network. The smaller base stations 1 16, 1 18 and 120 may also be connected to the network 1 13, for example by a separate gateway function and/or via the controllers of the macro level stations. The base stations 116, 1 18 and 120 may be pico or femto level base stations or the like. In the example, stations 1 16 and 1 18 are connected via a gateway 1 1 1 whilst station 120 connects via the controller apparatus 108. In some embodiments, the smaller stations may not be provided. Smaller base stations 1 16, 1 18 and 120 may be part of a second network, for example WLAN and may be WLAN APs.

A possible mobile communication device will now be described in more detail with reference to Figure 2 showing a schematic, partially sectioned view of a communication device 200. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device 200 may receive signals over an air or radio interface 207 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 2 transceiver apparatus is designated schematically by block 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A mobile device is typically provided with at least one data processing entity 201 , at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 204. The user may control the operation of the mobile device by means of a suitable user interface such as key pad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto. The communication devices 102, 104, 105 may access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on. Signalling mechanisms and procedures, which may enable a device to address in-device coexistence (IDC) issues caused by multiple transceivers, may be provided with help from the LTE network. The multiple transceivers may be configured for providing radio access to different radio technologies.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP

specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and provide E-UTRAN features such as user plane Packet Data Convergence/Radio Link Control/Medium Access Control/Physical layer protocol (PDCP/RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system comprise those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide

Interoperability for Microwave Access). A base station can provide coverage for an entire cell or similar radio service area. The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties. Another example of a suitable communications system is the 5G concept. Network architecture in 5G may be similar to that of the LTE-advanced. 5G may use multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates. It should be appreciated that future networks may utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

Hybrid automatic repeat request (HARQ) procedure is an example of an error control method for data transmission used in communication systems. In current LTE and LTE- Advanced networks, the maximum number of hybrid automatic repeat request (HARQ) processes that are allocated to a UE in the UL and in the DL for a given carrier may be fixed. LTE assumes a fixed HARQ round-trip time (RTT) and the maximum number of allowed HARQ process IDs matches this RTT. This ensures that there is no HARQ stall, i.e., a UE does not run out of HARQ processes and thus the base station is able to keep transmitting to the same UE in every TTI.

In Dual Connectivity (DC) and Carrier Aggregation (CA), where a user can receive/transmit data from/to multiple cells (e.g. a Primary cell, referred to as PCell and a secondary cell, referred to as Scell) in the DL/UL, the user may be allocated separate HARQ processes by each cell independently.

In future 5G systems, a centralized baseband (baseband pooling deployments) and cloud RAN architecture may be utilised where the HARQ RTT can vary considerably. In such a case, a configurable number of HARQ processes may be provided in order to improve robustness to variations in fronthaul latency.

When a UE is multiply connected, i.e., when a UE independently receives DL data from, or transmits UL data to, two or more cells simultaneously, current LTE & LTE-Advanced networks allocate the UE separate & independent HARQ processes in each cell.

Figure 3 shows a case where a macro cell and small cells (using baseband pooling and remote radio heads (RRH)) have different HARQ RTTs due to the additional front-haul latency to the RRH.

In a system as shown in Figure 3, a CA UE is receiving DL data from both a macro eNodeB and a RRH that is connected to the macro eNB via a fronthaul link with a one-way fronthaul delay of 2 TTIs as shown.

The HARQ RTT for DL packets transmitted by the Macro enodeB is less than that of the DL packets transmitted by the small cell by 4 TTIs. In this example, the Macro enodeB needs 6 HARQ processes, whereas, RRH based small cell needs 10 HARQ processes to prevent HARQ stalling. Static configuration of a maximum number of HARQ processes per cell across the entire network may not address this problem since different cells may experience different HARQ round-trip delays. Current LTE HARQ design may limit the ability to constantly transmit data on the air interface owing to the limit on the number of HARQ processes per carrier enforced by the 3GPP specifications. US patent publication no. 20040233887 proposes that data streams of a plurality of services should use a common HARQ process. In this way, the buffer to be provided on the receive side for the HARQ process may be reduced in size.

US patent publication no. 201 10276852 notes that the storage requirement per HARQ process may vary over time due to dynamic transport sizes so that a HARQ process with large memory requirements may benefit from memory unused by other active HARQ processes with smaller memory requirements and proposes methods to economize HARQ buffer management memory and strategies for discarding suitably identified data. Figure 4 shows a flowchart of an example method of providing a common HARQ buffer pool for a given UE receiving its data from multiple cells using the carrier aggregation method. In a first step, the method comprises providing a plurality of automatic repeat request (ARQ) processes associated with a user device and at least two cells associated with the user device.

In a second step the method comprises determining an automatic repeat request, from the plurality of automatic repeat request processes.

In a third step, the method comprises causing a transmission to the user device using the determined automatic repeat request process. The automatic repeat request process maybe a hybrid automatic repeat request (HARQ) process. The automatic repeat request process may be a stop and wait (SAW) process.

The user device may be a CA UE associated with a PCell and SCell, or a UE using carrier aggregation from more than two cells.

The at least two cells may use the same or different radio access technology or interfaces, such as but not limited to, LTE and 5G, LTE and LTE, 5G and 5G , respectively. The 5G radio access technology may in turn be a wide-area technology below 6 GHz, cmwave or mmwave technologies.

The at least two cells may be either co-located or geographically separated.

A method as described with reference to Figure 4 may be applicable to synchronous and asynchronous HARQ operation. A method as described with reference to Figure 4 may be applicable to FDD and TDD system. The method as described with reference to Figure 4 may also be applicable to UEs not operating in CA mode, but using different services on 5G network wherein, each of the services experience different HARQ round trip times owing to network slicing, e.g., based on QoS or QoE constraints. That is, the plurality of automatic repeat request process may be associated with a user device and a plurality of services (e.g. NRT, RT, streaming, etc). The plurality of services may experience different HARQ RTTs due to network slicing in 5G architecture.

The following is described with reference to HARQ process. However, any suitable ARQ process may be used. Determining the HARQ process may comprises selecting an HARQ identifier, or identity information, associated with the HARQ process, e.g. determining a HARQ ID. The HARQ identifier may be selected from a plurality of HARQ identifiers, each ARQ identifier associated with a respective of the plurality of HARQ processes. In an embodiment, determining identity information may comprise selecting the next available identifier from the plurality of identifiers associated with the plurality of HARQ processes.

The plurality of identifiers may be a pool of HARQ IDs. A pool of HARQ IDs common to all cells the UE is receiving data from may be maintained per UE. In an example, whenever a new packet is scheduled for transmission from the Pcell or Scell, the next available HARQ ID is picked dynamically from this pool.

Alternatively or in addition, the method may comprise determining a plurality of subsets of the plurality of automatic repeat request processes, each subset associated with a respective one of the at least two cells. The subsets may be determined semi-statically. That is, the number of HARQ process in a subset may be variable.

Determining the automatic repeat request process for a cell may comprise selecting an automatic repeat request identifier from a plurality of automatic repeat request identifiers, each identifier associated with a respective one of the plurality of automatic repeat request processes in the subset associated with the cell. That is, determining an HARQ process may comprise selecting the next available identifier from a plurality of identifiers associated with a first subset of the plurality of HARQ processes. The number of HARQ processes in the first subset may be variable. That is, the plurality of HARQ processes may be semi-statically partitioned between the at least two cells. As an example, there may be a semi-static partitioning of the common HARQ ID pool between the at least two cells associated with a UE.

The number of HARQ processes in the first subset may be determined in dependence on at least one of transport block size (TBS) and HARQ round trip time (RTT). For example, the semi-static partitioning can be adapted based on changes in the achievable TBS per scheduled instance and RTT of the connected cells. The change in the number of HARQ- processes associated with each connected cell over time may in addition or alternatively, be dependent on channel conditions, load-per-cell and varying front-haul latencies as a DC connected UE changes its Pcell and Scell(s) due to mobility.

This semi-static partitioning allows the schedulers of the connected cells of the UEs to work independently of each other in the fast TTI time-scale. A coordination of the semi-static partitioning over a slower time-scale may be provided to adapt the semi-static splitting of the common HARQ ID pool. For example, a first cell may provide information to at least one cell of the at least two cells for use in determining the number HARQ processes in a first subset. The information may comprise average transport block size when scheduled, the HARQ round-trip time, and the average time between successive scheduling instances of the UE on that cell.

The method provides baseband pooling with inter-site CA but using a common HARQ id pool across both Pcell and Scell

TBS/RTT is a single metric that may be used to determine the number of HARQ processes in a first subset, e.g. the semi-static partitioning. TBS is the UE's average TBS on a link with a given cell when it is scheduled and RTT is the HARQ round-trip-time on that link. It may be optimal to allocate HARQ ids in the descending order of TBS/RTT of the different links, subject to the condition that each link, or cell, is allocated only as many HARQ IDs so as to not result in a HARQ stall on that link. Note that the number of HARQ IDs needed to not result in a HARQ stall on a given link depends on how often the UE is scheduled on that link. If the RTT is Λ/ TTIs and the UE is scheduled every P TTIs, then the number of HARQ IDs needed to prevent HARQ stall is N/P.

The following shows a derivation of why TBS/RTT is a suitable metric, where

TBSi, TBS ₂ is the TBS achievable on Link 1 and Link 2, respectively, RTT1 , RTT ₂ is the HARQ Round Trip Time on Link 1 and Link 2, respectively and NumHarqi , NumHarq ₂ is the number of HARQ Ids allocated to Link 1 and Link 2 . In a first case, it is assumed that there is a single UE and the UE is scheduled in every TTI on both links. The Total Number of HARQ Ids/Processes available across both links is assumed to be a constant

NumHarq _T otai = NumHarqi + NumHarq ₂ The Total Throughput is proportional ) + TBS ₂ *mm(NumHarq ₂ IRTT ₂ A )

Assuming NumHarqi/ RTT1 <1 and NumHarq ₂ /RTT ₂ <1 and replacing NumHarq ₂ by NumHarq _T otai - NumHarqi, we obtain

Total Throughput TBS *{NumHarqilRTTi)+ TBS ₂ * (NumHarqTotai - NumHarqi) I RTT ₂ i.e., Total Throughput NumHarqi *( TBS1/RTT1 - TBS ₂ /RTT ₂ ) + TBS ₂ /RTT ₂ If TBSi/RTTi > TBS2 /RTT2

Total throughput increases as NumHarqi increases, for as long as NumHarqi else

Total throughput decreases as NumHarqi increases, or in other words,

Total throughput increases as NumHarq ₂ increases, for as long as NumHarq ₂

<=RTT ₂

Using this approach, for example, for RTT1 = 10, RTT2 = 15, TBS1:TBS2 = 1:10, we can achieve a gain of 65.5% over a static equal split of HARQ processes.

As Maximum number of HARQ processes are used for link 2, in spite of higher RTT, we observe significant gains.

As a second case, we consider a situation with multiple UEs, where UEs may not be scheduled in every TTI. Considering a situation where a UE is scheduled every Ni TTIs on Link 1 and on every N2 TTIs on Link 2, the UE's throughput is proportional to

( TBSi/ Ni) *min (Ni ^* NumHarqi/RTTi, 1 ) + { TBS ₂ /N ₂ )*mm (N ₂ ^* NumHarq ₂ /RTT ₂ , 1 )

Assuming Ni ^* NumHarqi/RTTi <1 and N ₂ ^* NumHarq ₂ /R TT ₂ < 1

Total UE Throughput TBSi*(NumHarq ₁ /RTT ₁ )+ TBS ₂ * ( NumHarq ₂ 1 R TT ₂ ) The highest achievable throughput is TBSi/ Ni + TBS ₂ /N ₂ Fewer HARQ Ids are needed on each link due to a reduction in the number of scheduling opportunities over a given duration. Hence, the regime for HARQ pooling benefits is much smaller than before.

However, in the applicable regime, optimal HARQ ID Allocation is still dependent on TBS/RTT ratio as earlier and is not impacted by Ni , N2 If TBS ₁ /RTT ₁ >= TBS ₂ /RTT ₂

Total throughput increases as NumHarqi increases as long as NumHarqi <=RTTi/Ni else

Total throughput decreases as NumHarqi increases, or in other words,

Total throughput increases as NumHarq ₂ increases, as long as NumHarq ₂ <=RTT ₂ /N ₂

For a synchronous HARQ link, the number of synchronous HARQ processes are set equal to the RTT. The period of synchronous HARQ operation (p) may be different from that of RTT, due to, for example, deployment of baseband processing in the cloud with potentially different HARQ RTTs. The single-UE peak throughput on a single link (assuming no CA dual connectivity) with synchronous HARQ is proportional to

, TBS*min(NumHarq,p)

Throughput oc ^ψψ

p*ceil(— )

This equation follows from the observation that, over a window of p*ceil(RTT/p) TTIs, the number of HARQ IDs or p can be scheduled, whichever is smaller.

In the case of synchronous HARQ, the total throughput of a aE using two links with different TBSs (TBS1 and TBS2) and different RTTs (RTT1 and RTT2) is proportional to

Total UE ThroughputK ^rB5l * ^min(N _fi ^ ^g/Dl ' ^p) ₊ TB^ UHARQID,*

p*ceil— p*ceil j

Thus the total UE throughput is maximized by using as many HARQ IDs as possible on the link with the larger value of

TBS

p *ceu

p

up to a maximum of p. This term may be referred to as the decision metric.

A method such as that described above with reference to Figure 4 may allow for a dynamic increase or decrease in the number of HARQ buffers per connected-cell using semi-static partitioning, keeping the total number of HARQ-processes-per-UE constant. This may result in more efficient HARQ memory management primarily at the UE, since network hardware is not memory constrained. Figure 5 shows an example of a pool of n HARQ processes which are provided for a UE in CA with a Pcell and an Scell. The pool of HARQ process is semi-statically partitioned. A first subset of the pool of HARQ processes is associated with the Pcell and a second subset of the pool of HARQ processes is associated with the Scell. In snapshot 1 , 3 HARQ process are associated with the Pcell and n-3 HARQ processes are associated with an Scell. In snapshot 2, 5 HARQ processes are used by the Pcell and n-5 HARQ processes are associated with the Scell.

To realize the gains from this application, a larger number of bits are needed to identify the pooled HARQ identifier when compared to the static split. Thus the disadvantage of the HARQ pooling concept is that the number of bits needed to identify the HARQ process in the control signaling for conveying scheduling information should be larger to account for the larger pool of HARQ processes. In the LTE method of using separate HARQ ids per link/carrier, if the number of HARQ ids per carrier is n, and if the UE is capable of aggregating m carriers, the number of bits needed to convey the HARQ process is log ₂ (w)] and is not dependent on the number of carriers aggregated. However, in the HARQ pooling concept, assuming that the total number of HARQ processes configured per UE across all cells is nm, then | ^~ log ₂ (ron)] number of bits would be needed to convey the HARQ process identifier.

In the semi-static partitioning embodiment, for transmissions from the Pcell, the next available HARQ ID will be selected from the HARQ IDs associated with the first subset of HARQ processes. For transmissions from the Scell, the next available HARQ ID from the HARQ IDs of the HARQ processes of the second subset of HARQ processes will be selected.

CA UE throughput may be improved by ensuring constant data transmission from multiple cells to which UE is connected, without imposing additional UE HARQ buffer memory requirement.

Retransmissions may be performed from any cell, e.g., when there is a change in Scell or when the UE has poor channel conditions on the Scell or when the Scell is congested, retransmissions may be performed from the Pcell.

A lower category UE designed with smaller number of HARQ buffers may effectively operate as if it were a higher category UE with a larger number of HARQ processes in total, as compared to the current state-of-the-art where separate HARQ processes need to be maintained in a multiply connected UE.

The method may be applicable to Multi-connectivity in case of 5G. As part of future 5G standards, the number of bits needed for HARQ Identifier will need to be specified such that it is larger than in 3GPP LTE and also needs to account for the maximum number of multiple cells anticipated to be connected to the UE.

This method is applicable in case of LTE-A Evolution, i.e., LTE CA Enhancements beyond 5CC (3GPP Release 13), in which also there exists a need for better soft buffer

management to avoid requiring UEs to support a large number of HARQ processes to realize the gains from CA with more than 5 CCs.. Figure 6 shows single-UE peak throughput gains from HARQ ID pooling (with 16 HARQ IDs in a pool) compared to a static split of 8 HARQ IDs for each cell link. The UE is assumed to have identical channel conditions in the two carriers. Throughput with static split of 8 HARQ IDs for each link is calculated as follows: If RTT <=8 TTIs, then 100% of the throughput is realized for that link, else the throughput realized is a fraction 8/RTT of the full throughput for that link. Finally, the throughput realized as a fraction of the single-link peak throughput possible is given by the sum of the throughput fractions of the two links of that UE.

The throughput realized as a fraction of the single-link peak throughput possible for common HARQ ID pool is calculated as follows: If sum of the RTT of the two links <=16 TTIs, then throughput fraction is 2, else it is 1 +(16-min(RTT1 ,RTT2))/max(RTT1 , RTT2), where RTT1 and RTT2 are the round-trip times of the two links.

Figure 6 shows that no gains may be achieved when the RTT is <=8 TTIs in both the links. The largest gains may be achievable when one of the links has very low RTT and the other of the links has a large RTT. Unused HARQ IDs from the link with small RTTs may be used for the link with large RTTs.

Gains are symmetric, i.e., gains for RTT1 =x, RTT2= y is the same as that for RTT1 =y and RTT2=x. No gains are achieved along the diagonal, RTT1 =RTT2 =x, because a symmetric split of the HARQ IDs is optimal in this case. Gains are also achieved when both RTTs are > 8 ms but different from each other. This is coming from using as many HARQ IDs as possible on the link with the lower RTT, thus reusing the HARQ IDs more often than when there is a static split.

It should be understood that each block of the flowcharts of the Figures and any combination thereof may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry.

The method may be implemented on a mobile device as described with respect to figure 2 or control apparatus as shown in Figure 7. Figure 7 shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a RAN node, e.g. a base station, (e) node B or 5G AP, a central unit of a cloud architecture or a node of a core network such as an MME or S-GW, a scheduling entity, or a server or host. The method may be implanted in a single control apparatus or across more than one control apparatus. The control apparatus may be integrated with or external to a node or module of a core network or RAN. In some embodiments, base stations comprise a separate control apparatus unit or module. In other embodiments, the control apparatus can be another network element such as a radio network controller or a spectrum controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus 300 can be arranged to provide control on communications in the service area of the system. The control apparatus 300 comprises at least one memory 301 , at least one data processing unit 302, 303 and an input/output interface 304. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The receiver and/or the transmitter may be implemented as a radio front end or a remote radio head. For example the control apparatus 300 or processor 201 can be configured to execute an appropriate software code to provide the control functions. Control functions may comprise providing a plurality of automatic repeat request processes associated with a user device and at least two cells associated with the user device, determining an automatic repeat request process, from the plurality of automatic repeat request processes and causing a transmission to the user device using the determined automatic repeat request process.

Alternatively, or in addition, control functions may comprise receiving, at a user device associated with at least two cells, a transmission from a first cell associated with the user device using an automatic repeat request process, the automatic repeat request process comprising an automatic repeat request process determined from a plurality of automatic repeat request processes associated with the user device and with the at least two cells.

It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

It is noted that whilst embodiments have been described in relation to LTE-A and DC systems, similar principles maybe applied in relation to other networks and communication systems, in particular 5G and multi-connectivity. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The embodiments of this invention may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

Embodiments of the inventions may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a

semiconductor substrate.

The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.