EP3350936A1

EP3350936A1 - Method, system and apparatus

Info

Publication number: EP3350936A1
Application number: EP15766134.9A
Authority: EP
Inventors: Ahmad AWADA; Fasil BERHANU TESEMA; Ingo Viering
Original assignee: Nokia Solutions and Networks Oy
Current assignee: Nokia Solutions and Networks Oy
Priority date: 2015-09-16
Filing date: 2015-09-16
Publication date: 2018-07-25
Also published as: WO2017045710A1

Abstract

There is provided a method comprising determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and causing a joint transmission of at least one first signal type using the first subset of cells.

Description

DESCRIPTION

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 management of intra-frequency cells in multi- connectivity environment such as 5G.

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 determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and causing a joint transmission of at least one first signal type using the first subset of cells.

The first signal type may be at least one of a control signal and a data signal.

The first signal type may be a control signal, and determining the first subset of cells may comprise determining the minimum number of cells in the first subset such that a channel threshold value is met. The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel.

The method may comprise receiving information from the user device to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The indication of the at least one cell may be determined in dependence on the signal quality of the channel on which the signal is transmitted. The method may comprise receiving channel state information associated with the at least one cell from the user device. The method may comprise providing resource utilization information to the user device for use in determining the indication of the at least one cell.

The user device may provide channel state information for each of the plurality of cells and the method may comprise determining the first subset of cells in dependence on the channel state information.

The method may comprise determining the plurality of cells configured for joint scheduling for the user device in dependence on measurement reports received from the user device. The method may comprise determining a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device and causing a joint transmission of a second signal type using the second subset of cells.

The first signal type may be one of a control signal and a data signal and the second signal type may be the other of the control signal and the data signal.

Coordination of joint transmission for the first subset of cells may be separate to the coordination of joint transmission for the second subset of cells. In a second aspect there is provided a method comprising receiving a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

The first signal type may be a control signal, and the method may comprise determining the first subset of cells, wherein determining the first subset of cells comprises determining the minimum number of cells in the first subset such that a channel threshold value is met.

The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel. The method may comprise providing information to a network entity associated with the plurality of cells, the information to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells. The method may comprise determining the indication of the at least one cell in

dependence on the signal quality of the channel on which the signal is transmitted.

The method may comprise providing channel state information associated with the at least one cell to the network entity.

The method may comprise receiving resource utilization information from the network entity for use in determining the indication of the at least one cell.

The method may comprise providing channel state information to the network entity for each of the plurality of cells for use in determining the first subset of cells.

The plurality of cells configured for joint scheduling for the user device may be determined in dependence on measurement reports received from the user device. The method may comprise receiving a joint transmission of a second signal type using a second subset of cells.

Coordination of joint transmission for the first subset of cells may be separate to the coordination of joint transmission for the second subset of cells.

In a third aspect there is provided an apparatus, said apparatus comprising means for determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and means for causing a joint transmission of at least one first signal type using the first subset of cells.

The first signal type may be a control signal, and determining the first subset of cells may comprise determining the minimum number of cells in the first subset such that a channel threshold value is met. The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel. The apparatus may comprise means for receiving information from the user device to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The indication of the at least one cell may be determined in dependence on the signal quality of the channel on which the signal is transmitted.

The apparatus may comprise means for receiving channel state information associated with the at least one cell from the user device. The apparatus may comprise means for providing resource utilization information to the user device for use in determining the indication of the at least one cell.

The user device may provide channel state information for each of the plurality of cells and the apparatus may comprise means for determining the first subset of cells in dependence on the channel state information.

The apparatus may comprise means for determining the plurality of cells configured for joint scheduling for the user device in dependence on measurement reports received from the user device.

The apparatus may comprise means for determining a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device and means for causing a joint transmission of a second signal type using the second subset of cells. The first signal type may be one of a control signal and a data signal and the second signal type may be the other of the control signal and the data signal.

In a fourth aspect there is provided an apparatus, said apparatus comprising means for receiving a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device. The first signal type may be at least one of a control signal and a data signal.

The first signal type may be a control signal, and the apparatus may comprise means for determining the first subset of cells, wherein determining the first subset of cells comprises determining the minimum number of cells in the first subset such that a channel threshold value is met.

The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel.

The apparatus may comprise mean for providing information to a network entity associated with the plurality of cells, the information to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The apparatus may comprise means for determining the indication of the at least one cell in dependence on the signal quality of the channel on which the signal is transmitted. The apparatus may comprise means for providing channel state information associated with the at least one cell to the network entity.

The apparatus may comprise means for receiving resource utilization information from the network entity for use in determining the indication of the at least one cell.

The apparatus may comprise means for providing channel state information to the network entity for each of the plurality of cells for use in determining the first subset of cells. The plurality of cells configured for joint scheduling for the user device may be determined in dependence on measurement reports received from the user device.

The apparatus may comprise means for receiving a joint transmission of a second signal type using a second subset of cells.

The first signal type may be one of a control signal and a data signal and the second signal type may be the other of the control signal and the data signal. Coordination of joint transmission for the first subset of cells may be separate to the coordination of joint transmission for the second subset of cells.

In a fifth aspect there is provide 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 determine at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and cause a joint transmission of at least one first signal type using the first subset of cells.

The first signal type may be a control signal, and determining the first subset of cells may comprise determining the minimum number of cells in the first subset such that a channel threshold value is met.

The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel. The apparatus may be configured to receive information from the user device to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The apparatus may be configured to receive channel state information associated with the at least one cell from the user device. The apparatus may be configured to provide resource utilization information to the user device for use in determining the indication of the at least one cell.

The user device may provide channel state information for each of the plurality of cells and the apparatus may comprise means for determining the first subset of cells in dependence on the channel state information. The apparatus may be configured to determine the plurality of cells configured for joint scheduling for the user device in dependence on measurement reports received from the user device. The apparatus may be configured to determine a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device and cause a joint transmission of a second signal type using the second subset of cells.

Coordination of joint transmission for the first subset of cells may be separate to the coordination of joint transmission for the second subset of cells. In a sixth aspect there is provided 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 a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

The apparatus may be configured to provide information to a network entity associated with the plurality of cells, the information to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The apparatus may be configured to determine the indication of the at least one cell in dependence on the signal quality of the channel on which the signal is transmitted. The apparatus may be configured to provide channel state information associated with the at least one cell to the network entity.

The apparatus may be configured to receive resource utilization information from the network entity for use in determining the indication of the at least one cell.

The apparatus may be configured to provide channel state information to the network entity for each of the plurality of cells for use in determining the first subset of cells. The plurality of cells configured for joint scheduling for the user device may be determined in dependence on measurement reports received from the user device.

The apparatus may be configured to receive a joint transmission of a second signal type using a second subset of cells.

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 determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and causing a joint transmission of at least one first signal type using the first subset of cells.

The first signal type may be a control signal, and determining the first subset of cells may comprise determining the minimum number of cells in the first subset such that a channel threshold value is met. The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel. The process may comprise receiving information from the user device to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells. The indication of the at least one cell may be determined in dependence on the signal quality of the channel on which the signal is transmitted.

The process may comprise receiving channel state information associated with the at least one cell from the user device.

The process may comprise providing resource utilization information to the user device for use in determining the indication of the at least one cell.

The process may comprise determining the plurality of cells configured for joint scheduling for the user device in dependence on measurement reports received from the user device.

The process may comprise determining a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device and causing a joint transmission of a second signal type using the second subset of cells. The first signal type may be one of a control signal and a data signal and the second signal type may be the other of the control signal and the data signal.

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 a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

The first signal type may be at least one of a control signal and a data signal. The first signal type may be a control signal, and the method may comprise determining the first subset of cells, wherein determining the first subset of cells comprises determining the minimum number of cells in the first subset such that a channel threshold value is met. The channel threshold value may be at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel.

The process may comprise providing information to a network entity associated with the plurality of cells, the information to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

The process may comprise determining the indication of the at least one cell in

dependence on the signal quality of the channel on which the signal is transmitted. The process may comprise providing channel state information associated with the at least one cell to the network entity.

The process may comprise receiving resource utilization information from the network entity for use in determining the indication of the at least one cell.

The process may comprise providing channel state information to the network entity for each of the plurality of cells for use in determining the first subset of cells.

The plurality of cells configured for joint scheduling for the user device may be determined in dependence on measurement reports received from the user device.

The process may comprise receiving a joint transmission of a second signal type using a second subset of cells. The first signal type may be one of a control signal and a data signal and the second signal type may be the other of the control signal and the data signal.

In a ninth aspect there is provided a computer program product for a computer, comprising software code portions for performing the steps the method of the first aspect and/or second when said product is run on the computer. 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 plot of SINR against distance for LTE CoMP and 5G multi-connectivity;

Figure 4 shows a schematic diagram of an example network architecture; Figure 5 shows a flowchart of an example method for transmitting in a multi-connectivity environment;

Figure 6 shows a flowchart of an example method for receiving transmission in a multi- connectivity environment;

Figure 7 shows a schematic diagram of an example active set member coordination; Figure 8 shows an example signalling flowchart; Figure 9 shows an example signalling flowchart; Figure 10 shows an example signalling flowchart; Figure 1 1 shows an example signalling flowchart;

Figure 12 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 1 13 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 1 16, 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.

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.

Another example of a suitable communications system is the 5G concept. Network architecture in 5G may be similar to the general principle of LTE-advanced but with functions performed across different entities. 5G may use multiple input - multiple output (MIMO) antennas, 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 will most probably 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.

Multi-connectivity refers to a use case where a user is served by one or more cells that are co-ordinated based on certain criteria. The set of serving cells of a user may be referred to as an "active set" (AS) which is similar to that used in 3G and described below. Multi-connectivity that use an AS for co-ordinating transmission of both control and data signals has been proposed in 5G. Co-ordination of transmission of data signals targets throughput improvement whereas that of control signals targets mobility robustness. However, the optimal AS (e.g. the optimal size of an AS and/or the optimal members of an AS) that enable best performance on throughput may not be the same as the optimal AS that enables best performance on mobility robustness. Furthermore, as discussed below, an AS may be updated based on average measurements and trigger events that are slow compared to the fast change of the channel. Thus, separate and faster co-ordination of member cells of the AS for the data and control signals may be desirable. In LTE, investigation on Cooperative Multi-Point (CoMP) addresses multi-connectivity solutions.

CoMP allows the optimization of transmission and reception from multiple distribution points, which could be either multiple cells or Remote Radio Heads (RRH). One of the major objectives of CoMP is to maximize user throughput and system capacity through mitigation of inter-cell interference. Some of the transmission schemes adopted by CoMP are non-coherent Joint Transmission (JT), coherent JT and Dynamic Point Selection (DPS). In LTE CoMP, only one of the co-operating cells, referred to as Primary Cell (PCell), is responsible for control signalling and radio link monitoring by a UE. If the control on the PCell has radio problems, the other cells ("secondary cells", SCells) cannot serve as a fall back. So this arrangement may not improve the control-channel robustness, and thus will not improve mobility.

The co-operating set in CoMP is targeted for co-ordinating transmission of data signals only. Moreover, for control signals there is a single link to the PCell in the cooperating set. Consequently, the mobility challenge is equivalent to single-connectivity because the terminal purely depends on the link to the PCell which is changed by a conventional handover. As it will be described later on, for 5G it is required that the mobility robustness is improved by co-ordinated transmission in the C-plane as well. Figure 3 illustrates the benefits and drawbacks of the LTE CoMP solution, and the mobility advantages in case of C-plane multi-connectivity in 5G.

As shown in Figure 3, LTE CoMP may improve the SINR on the data channel (and thereby the throughput), but not on the control channels. However, with 5G multi- connectivity gain may be provided to the control channels as well, which in turn improve mobility by resolving RLFs.

3G Soft Handover defines an active set (AS), with appropriate triggers to update the active set. For instance, 25.331 has defined a first trigger event "1 A" as (simplified) Mn+ Ocn> m^Ms)+ OJ _add

seA

where the symbol A is used for the active set, i.e. A is a set consisting of a number of serving cells s1 , s2,....

Such a condition expires if the measurement Mn of a "new" cell n is offset better than the measurement of the best cell in the current active set. The expiry would trigger a measurement report to the base station, and the base station would add the new cell n to the active set.

Here, in contrast to a typical hysteresis value Off_add \s likely to be a negative value, i.e. you would add a cell to the active set, even if it is still weaker than the best cell. Similar to the addressed multi-connectivity case in 5G, this comes along without risk since the best cell is kept and not dropped as in the case of a single connectivity handover. Equivalent to the definition of 1 A trigger event in 3G, there exists a second trigger event 1 B to remove a cell from the active set. The network removes a cell sO from the active set

A when a measurement report is received which has been triggered by the following condition:

Μ Ο+ OC® < mao(Ms)+ Off_nmove

seA

i.e. a cell would be removed if it falls significantly below the best cell (for a certain time to trigger). This condition to be fulfilled for a certain time period ("time to trigger"), whereas in every time instance the condition is evaluated using the best of all cells.

In 3G there is only one active set which does not differentiate between user data and control planes. Moreover, the active set is updated using layer 3 (L3) averaged

measurements and in turn cannot cope with fast channel variations.

In LTE, three types of instantaneous feedback reports are defined for the radio resource management: Channel Quality Indicator (CQI), Rank Indicator (Rl) and Pre-coding Matrix Indicator (PM I). The CQI feedback is reported by the UE to the network to help the network decides on link adaptation parameters that it should use for transmitting to the UE. It is a number index that corresponds to the Modulation and Coding Scheme (MCS) for which the downlink Block Error Rate (BLER) shall not exceed a targeted threshold. Rl and PMI are reported only when the UE is operating in MIMO modes. Rl refers to the UE's proposal for the number of layers (streams) to be used in spatial multiplexing. Rl can have values 1 to 4 for 4 by 4 MIMO configurations. On the other hand, PMI provides information about the preferred pre-coding matrix for a set of pre-coding codebooks. Pre- coding codebook refers to a quantized codebook set that allows selection of antenna weights (vector or matrix) from a fixed number of possibilities. The transmission mode where the U E reports only the Rl but no PMI is called open-loop spatial multiplexing whereas the transmission mode where the UE reports both the Rl and PMI is called closed-loop spatial multiplexing. The evolution to 5G Mobile networks will be characterized by increased number of wireless devices and diverse applications with very high performance requirements. Some of the key enablers to realize the aforementioned challenge for future networks are Ultra Dense Network (UDN) deployments and centralized processing.

In order to satisfy ultra-high reliability requirement of future networks, it is desirable that 5G multi-connectivity solutions guarantee resolution of all mobility failures by increasing robustness in the control signals. Unlike the existing concepts such as CoMP

transmissions, 5G multi-connectivity schemes rely on the fact that the transmissions from co-operating cells are co-ordinated not only for user data plane but also for control plane. For 5G multi-connectivity, the active set management schemes mentioned under 3G soft handover have been investigated based on 5G context and requirements. Moreover adaptive schemes of configuring add/remove triggers have been evaluated. However, the configured AS is used to co-ordinate transmission of both the control and data signals.

The following is described with reference to a radio access architecture which comprises a cloud architecture where access points are connected to a central unit that undertakes the basic Media Access Control and physical layer functionalities. Figure 4 shows a schematic diagram of such an example architecture. In Figure 4, the access points have only Radio Frequency (RF) functionalities similar to Remote Radio Heads In the following, the term "cell" is used as a general expression for an antenna array mounted on a single site.

The 5G multi-connectivity methodology described above assumes that the cells in the AS that are used for coordination of transmission of mobility related control signals and data signals are the same. However, the requirements for resolving mobility problems and for achieving good performance in throughput are not the same. For example, one of the major measures of mobility problem is Radio Link Failure (RLF). The UE monitors regularly the downlink radio link quality by comparing it with out-of-sync and in-sync thresholds. These thresholds are expressed in terms of Block Error Rate (BLER) on the Physical Downlink Control Channel (PDCCH) that is transmitted from the serving cell(s) in the active set. On the other hand, the UE data in the downlink direction is carried on the Physical Downlink Shared Channel (PDSCH) and the throughput performance depends on the co-ordination of member cells of the AS, Channel state Information (CSI) feedbacks such as CQI/RI/PMI, packet retransmission schemes and the time-frequency resource allocation scheme. Furthermore, the update of AS is relatively slow because AS triggers are based on averaged measurements and slow change of the channel. The reason for this sluggish behaviour is the fact that AS updates are typically associated with significant signalling, not only on the air interface, but also in the backhaul, and therefore it is desirable to make the AS updates very solid and reliable avoiding AS updates due to fast fading or measurement outliers. We assume that the same mobility mechanisms will be used as in LTE, such as L3 filtering, HO margin, time to trigger. Figure 5 shows a flowchart of an example method of transmitting in a multi-connectivity environment. The method comprises, in a first step 520, determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device.

In a second step 540 the method comprises causing a joint transmission of at least one first signal type using the first subset of cells.

Figure 6 shows a flowchart of an example method of receiving transmission in a multi- connectivity environment. In a first step 620 the method comprises receiving a joint transmission of at least first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

The first signal type may be one or more of a signal or a control signal. Causing transmission may comprise coordinating transmission and signalling of the signal type on a respective channel.

A method such as that shown in figure 5 may optionally comprise determining a second subset of cells selected from the plurality of cells and causing a transmission on a second channel type using the second subset of cells. A method such as that shown in figure 6 may optionally comprise receiving a transmission on a second channel type from a second subset of cells, selected from the plurality of cells configured for joint scheduling for a user device. The first signal type may be one of a data signal and a control signal and the second signal type may the other of the data signal and the control signal. The coordination of joint transmission for the subset of cells is separate to the coordination of joint transmission of the second subset of cells.

A method such as that shown in Figures 5 and 6 may achieve faster and/or separate coordination of member cells of an AS for transmission of control signals and data signals. DL transmission is referred to. For each user device u, the plurality of cells configured for joint scheduling for a user device which may be referred to as a global AS, AS£. The plurality of cells, or global AS, may be built based on triggering events such as those discussed in 3G handover or 5G Multi-connectivity. The AS management trigger encompasses uses of add, remove and/or replace events based on averaged RSRP or RSRQ measurements at the UE. This may be a relatively slow process because the instability of measurements due to fast fading has to settle down and timers associated to the triggering events have to expire before an AS is updated. Consequently, the aforementioned procedure builds a stable member of the AS.

First and second subsets of cells of AS^ may be used to independently organize control AS and data AS. A subset of cells for control signals may be denoted by AS£. A subset of cells for data signals may be denoted AS° respectively. Update of AS£ and AS° is faster as compared to the global AS update in order to cope with fast change of the channel.

This is illustrated in Figure 3 which shows that the global AS AS^ changes slowly with time whereas the first and second subsets AS£ and AS° may change at much faster rate to cope with fast channel variations. Figure 7 shows example subsets AS£ and AS° of ASf; as the sets change over time. At the beginning of the time period, AS„ comprises cells 1 , 2 and 3. A first subset AS„ comprises cell 1 and a second subset ASu Comprises cells 1 and 2. At the end of the time period shown in figure 7, ASf; has been increased to comprise cells 1 , 2, 3, 4 and 5. The first subset of cells AS„ comprises cells 1 , 2 and 3 and the second subset ASu Comprises cells 1 , 2 3, 4 and 5. In the time taken for the global set to increase from 3 to 5 cells, the first and second subset changes three times

The mechanisms to select co-ordinating cells for the joint transmission of control and/or data signals are fast and use instantaneous (as well as potentially frequency resolved) measurements of the received powers (instead of wideband RSRP measurements), however only from inside the pre-configured global active set.

In an embodiment, the UE may decide (or at least propose) member cells for a subset of cells (e.g. AS£ and/or AS° ) based on a certain criteria. That is the UE may provide information to be used in determining a subset of cells, the information comprising an indication of at least one cell of the plurality of cells. AS£ and AS° may be selected from the global AS AS^ which has been decided by the network (based on measurement reports by the UE) on a slow time scale. Then the UE reports the proposed cell IDs corresponding to AS^ and AS° .

Figure 8 shows an example signalling flowchart in which a UE provides an indication of cells for use in determine a first subset of cells, in this example AS„. The network then causes a transmission (e.g. of the control signals) using the first subset of cells. Such a UE based approach is already applied within the existing MIMO schemes where the UE instantly proposes a PMI and Rl, plus a CQI fitting to the PMI/RI. In most of the cases the BS will follow this proposal. The UE would make its selection inside the global AS AS„ which is determined by the network on a slow time scale.

The indication of the at least one cell provided by the UE may be determined in dependence on the signal quality of the channel on which the signal is transmitted. As an example, when determining a subset of cells for transmission of control signals, ASfj the determining may comprise the following: Assuming non-coherent joint transmission among the cells in AS£, the signal quality of the control channel can be calculated, in terms of Signal to Interference plus Noise Ratio (SINR), as

_SINRc ₌ ^∑ceAS" ^Pc'^u where P_CjU is the instantaneous received power in the control channels from cell c to UE u and /V is noise power. The SINR„ can be used to emulate the signal quality of the link that the UE is monitoring. If SINR^j is below a certain targeted threshold Q_out it considers itself to be out-of-sync.

The UE may sweep through candidate cells for subset AS£ and determine the minimum size set that ensures SINRu to be greater than Q_out. Choosing the minimum size for AS^ ensures that control resources on the other members of ASf; are not unnecessarily wasted. Figure 8 shows UE-based signalling procedures between the UE and the network in order to decide AS£.

Alternatively, or in addition, determining a subset of cells for joint transmission of a data signal, AS° may comprise the following: Assuming similar power allocation scheme and non-coherent joint transmission, the SINR ls is

The UE may not be aware of the scheduler limitations as it does not have the scheduler scheme implemented at the UE side. Resource utilisation information may be provided to the user device for use in determining the indication of the at least one cell. For example, the network may configure transmission of resource utilization information (e.g. load) to the UE to substantiate UE's decision of AS°. The resource utilization information of all cells in the same cloud is available at the network since there is a central scheduler for a cloud. Thus, the network can use broadcast transmission to distribute resource utilization information to the users that are served in the same cloud.

The UE may sweep through all possible subsets of AS° that are combination of member cells of ASu and derives their corresponding SINR° values. Using the resource utilization information from the network and the computed SINR, the UE may select one optimal AS° subset and signal it to the network. Then the network may use the signalled AS° subset to co-ordinate transmission of data signals. This implementation may be extended by allowing the UE to select more than one candidate AS° subsets and signal it to the network. Then the network uses extra scheduling information to commit one of the candidate AS° subsets as an optimal one.

Figure 9 shows UE-based signalling procedures to decide AS° . The UE receives resource utilisation information form the network. The UE provides an indication of cells to be used in determining a subset of cells, here AS° . Note that the UE should send corresponding CSI information (CQI/PMI/RI) corresponding to the signalled AS° subset (s).

As an example, if a UE has 3 cells in the global AS with instantaneous signal strengths of -60dBm, -63dBm and -66dBm. The 2 stronger cells (with -60 and -63dBm) are rather empty cells, whereas the weak cell (with -66dBm) is pretty loaded. Interference from other cells plus noise adds up to -80dBm. Selecting the strongest 1 , 2 or 3 cells will lead to SINRs of 1 .18dB, 7.6dB and 22.4dB. As a consequence, from the UE perspective the decision would be to use all 3 cells for transmission (purely based on the SINR). However, in fact it might be better to use only the strongest 2 cells. The UE has to survive with an SINR of 7.6dB, but it would get much more resources since the overloaded 3^rd cell would add too many scheduler constraints. As such, the resource utilization information should be considered by the UE when deciding on the optimal AS° .

Alternatively, or in addition, configurations of the respective subsets of cells (e.g. AS„ and ASu ) may be undertaken at the network side. The network side may be a central entity for the set of cells that are connected to one cloud, e.g. a network entity that is associated with the plurality of cells configured for joint scheduling for a user device. In an

embodiment, the UE may provide channel state information associated with at least one cell of the plurality of cells, e.g. the UE may report signal quality indicators for channels and the network decides which member cells of AS^ are used for a respective subset of cells. In an example, if first and second subset of cells are being coordinated for control and data signals, i.e. AS„ and AS° , the UE may report channel state information for the control and data channel respectively . The determining of the subsets may thus be transparent to the UE.

There are no standardized feedbacks to make the network aware of out-of-sync and in- sync states of a UE. The network only becomes aware after a radio link failure is declared by the UE. Consequently, there is limited information at the network to act proactively on the decision of ASfj before the radio link failure. As a result, the optimistic solution is that the network uses all member of AS^ as ASfj. The disadvantage is that a few members of ASu might be enough to completely resolve RLFs and with bigger size of AS£ resources on the control channels are wasted. Note that it is unfortunately not possible to make the global AS smaller. Due to its sluggishness it has to be forward looking to make sure that any cell which may become relevant in the future is added early enough. The signalling and functionalities of network-based co-ordination on the control signals is shown in Figure 10. In this example, the network entity determines the first subset of cells ASfjand the subset is transparent to the user

For configuration of AS° , the network has information on signal quality as well as MIMO transmission scheme from CQI/PMI/RI feedbacks. Moreover, the information on the scheduler is available for a given cloud because the scheduler is central. Therefore, one option is to decide configuration of AS° independent of the scheduler. For example, configuring the best K cells of AS^ as elements of AS° . However, this method does not take into account the risk of resource wastage by configuring too many cells in AS° . A better option may be to include configuration of AS° into the problem formulation of the scheduler and solve the resource allocation as well as AS° .

This solution requires CQI feedback for different configuration of AS° from the UE. For example, a scheduler that uses "proportional-fair" scheme allocates a certain resource block to the user that maximizes the following ratio

ppRatio _ ^ u.

R_u

where r_u is the achievable bit rate for user u on the resource block for the given MCS and ASu ; and R_u is the average achieved throughput. If the size of the global active set has 4 member cells, then we have a total of 15 combinations of the member cells as AS° subsets. Extra 4 bits can be added to the bits that transmit a specific CQI/PMI/RI from the UE to the network in order to signal the corresponding AS° subsets. Figure 1 1 shows the signalling and functionalities of network-based co-ordination on the data signals. In this example, the UE provides an indication of cells and associated channel state information for use in determining a first subset of cells. The network entity determines the first subset of cells AS,? , which is transparent to the user.

Alternatively, or in addition, the two proposals described above may be combined. A UE- based proposal may be better in configuring AS£ . Thus, the UE decides the configuration of ASu by choosing the minimum AS size that guarantees the control signal quality to be above a targeted threshold Q_out, using, for example, a signalling flow such as that shown in figure 8 For configuration of AS° , the network-based proposal may have more insight on the tradeoff between throughput gain and risk of resource wastage. Thus, the idea of including problem of finding AS° into the scheduler problem is the better option, using e.g. a signalling flow such as that of figure 1 1 . It should be understood that each block of the flowchart 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 12. Figure 12 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 can be configured to execute an appropriate software code to provide the control functions.

Control functions may comprise determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device and causing a joint transmission of at least one first signal type using the first subset of 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 5G networks, similar principles maybe applied in relation to other networks and communication systems, for example, 5G networks. 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.

Claims

1 . A method comprising:

determining at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device; and

causing a joint transmission of at least one first signal type using the first subset of cells.

2. A method according to claim 1 , wherein the first signal type is at least one of a control signal and a data signal.

3. A method according to claim 2, wherein the first signal type is a control signal, and determining the first subset of cells comprises determining the minimum number of cells in the first subset such that a channel threshold value is met.

4. A method according to claim 3, wherein the channel threshold value is at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel.

5. A method according to any preceding claim, comprising:

receiving information from the user device to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

6. A method according to claim 5, wherein the indication of the at least one cell is determined in dependence on the signal quality of the channel on which the signal is transmitted.

7. A method according to claim 5 or claim 6 comprising receiving channel state information associated with the at least one cell from the user device.

8. A method according to any one of claims 5 to 7, comprising providing resource utilization information to the user device for use in determining the indication of the at least one cell.

9. A method according to any preceding claim, wherein the user device provides channel state information for each of the plurality of cells and comprising:

determining the first subset of cells in dependence on the channel state information.

10. A method according to any preceding claim, comprising determining the plurality of cells configured for joint scheduling for the user device in dependence on measurement reports received from the user device.

1 1 . A method according to any preceding claim, comprising:

determining a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device;

causing a joint transmission of a second signal type using the second subset of cells.

12. A method according to claim 1 1 , wherein the first signal type is one of a control signal and a data signal and the second signal type is the other of the control signal and the data signal.

13. A method according to claim 1 1 or claim 12, wherein coordination of joint

transmission for the first subset of cells is separate to the coordination of joint transmission for the second subset of cells.

14. A method comprising:

receiving a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

15. A method according to claim 14, wherein the first signal type is at least one of a control signal and a data signal.

16. A method according to claim 15, wherein the first signal type is a control signal, and comprising determining the first subset of cells, wherein determining the first subset of cells comprises determining the minimum number of cells in the first subset such that a channel threshold value is met.

17. A method according to claim 16, wherein the channel threshold value is at least one of a block error rate value and a signal to interference plus noise ratio value of a control channel.

18. A method according to any one of claims 14 to 17, comprising: providing information to a network entity associated with the plurality of cells, the information to be used in determining the first subset of cells, the information comprising an indication of at least one cell of the plurality of cells.

19. A method according to claim 18, comprising: determining the indication of the at least one cell in dependence on the signal quality of the channel on which the signal is

transmitted.

20. A method according to claim 18 or claim 19 comprising providing channel state information associated with the at least one cell to the network entity.

21 . A method according to any one of claims 18 to 20, comprising receiving resource utilization information from the network entity for use in determining the indication of the at least one cell.

22. A method according to any one of claims 14 to 21 , comprising providing channel state information to the network entity for each of the plurality of cells for use in determining the first subset of cells.

23. A method according to any one of claims 14 to 22, wherein the plurality of cells configured for joint scheduling for the user device is determined in dependence on measurement reports received from the user device.

24. A method according to any one of claims 14 to 23, comprising:

receiving a joint transmission of a second signal type using a second subset of cells.

25. A method according to claim 24, wherein the first signal type is one of a control signal and a data signal and the second signal type is the other of the control signal and the data signal.

26. A method according to claim 24 or claim 25, wherein coordination of joint

27. A computer program product for a computer, comprising software code portions for performing the steps of any of claims 1 to 26 when said product is run on the computer.

28. An apparatus comprising means for performing a method according to any one of claims 1 to 26.

29. 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:

determine at least a first subset of cells, selected from a plurality of cells configured for joint scheduling for a user device; and

cause a joint transmission of at least one first signal type using the first subset of cells.

30. An apparatus according to claim 29, wherein the first signal type is at least one of a control signal and a data signal.

31 . An apparatus according to claim 29 or 30, wherein the plurality of cells configured for joint scheduling for the user device is determined in dependence on measurement reports received from the user device.

32. An apparatus according to any one of claims 29 to 31 , configured to

determine a second subset of cells selected from the plurality of cells configured for joint scheduling for a user device; and

cause a joint transmission of a second signal type using the second subset of cells.

33. An apparatus according to claim 32, wherein the first signal type is one of a control signal and a data signal and the second signal type is the other of the control signal and the data signal.

34. An apparatus according to claim 32 or claim 33, wherein coordination of joint transmission for the first subset of cells is separate to the coordination of joint transmission for the second subset of cells.

35. 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 a joint transmission of at least one first signal type from a first subset of cells selected from a plurality of cells configured for joint scheduling for a user device.

36. An apparatus according to claim 35, wherein the first signal type is at least one of a control signal and a data signal.

37. An apparatus according to claim 35 or 36, wherein the plurality of cells configured for joint scheduling for the user device is determined in dependence on measurement reports received from the user device.

38. An apparatus according to any one of claims 29 to 31 , configured to receive a joint transmission of a second signal type using a second subset of cells.

39. An apparatus according to claim 38, wherein the first signal type is one of a control signal and a data signal and the second signal type is the other of the control signal and the data signal.

40. An apparatus according to claim 38 or claim 39, wherein coordination of joint transmission for the first subset of cells is separate to the coordination of joint transmission for the second subset of cells.