WO2021204250A1

WO2021204250A1 - Method and network device for coverage enhancement

Info

Publication number: WO2021204250A1
Application number: PCT/CN2021/086176
Authority: WO
Inventors: Yi GENG
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2020-04-10
Filing date: 2021-04-09
Publication date: 2021-10-14

Abstract

The present disclosure provides a method (400) in a network device. The method (400) includes: transmitting (410) a Channel State Information -Reference Signal, CSI-RS, to a terminal device via a beam from a first set of candidate beams, the first set including at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for Synchronization Signal and Physical Broadcast Channel 'PBCH', SSB, transmission.

Description

METHOD AND NETWORK DEVICE FOR COVERAGE ENHANCEMENT

TECHNICAL FIELD

The present disclosure relates to communication technology, and more particularly, to a method and a network device for coverage enhancement.

BACKGROUND

As commercial Unmanned Aerial Vehicle (UAV) applications become increasingly popular, mobile networks such as the 5 ^th Generation (5G) or Long Term Evolution (LTE) networks are required to support communications for aerial terminal devices (e.g., User Equipments, or UEs) , such as UAVs and UEs carried by passengers in commercial airplanes at low altitudes.

The existing mobile networks are designed for terrestrial broadband communications for e.g., users on the ground and in buildings, with antennas of network devices (or base stations) being down-tilted to optimize ground coverage and reduce inter-cell interference. At higher altitudes, there may be several challenges that could lead to a different radio environment from the ground, including e.g., Line-of-Sight (LOS) propagation and uplink interference, poor Key Performance Indicators (KPIs) caused by antenna sidelobes, and sudden drops in signal strengths.

Empirical measurements have shown that aerial radio channels exhibit different propagation characteristics from those of terrestrial radio channels. One distinct feature of the aerial radio channels is a higher likelihood of LOS propagation due to absence of obstacles in the sky. Fig. 1 shows an exemplary scenario of LOS propagation for a UAV. As shown, a UE 102 on the ground has no LOS link with any of

base stations

120, 122, and 124 due to blocking by the buildings, while a UAV 110 in the sky has an LOS link with each of the

base stations

120, 122, and 124. Due to the LOS propagation, the signal strength received at the UAV 110 becomes higher as a result of a reduced path loss. While a higher signal strength from a serving base station (e.g., base station 120) is desired, the UAV 110 may have LOS paths to a number of non-serving (or interfering) base stations (e.g., base stations 122 and 124) . As the

base stations

120, 122, and 124 may share the same radio resources, the increased likelihood of LOS paths to the non-serving base stations increases the interference at the UAV 110. A high level of interference may cause a low Signal to Interference plus Noise Ratio (SINR) , which makes it difficult for the UAV 110 to promptly receive and decode mobility management related messages (e.g., handover commands) . Further, as in many use cases the UAV 110 is required to transmit video feeds to its flight controller, imposing heavy uplink traffic load on the network, the UAV 110 may also generate more uplink interference to the

non-serving base stations

122 and 124.

Due to the down-tilted antennas at the base stations, UAVs and airplanes in the sky may be served by sidelobes of the antennas. The sidelobes give rise to a phenomenon known as scattered cell association, which is particularly noticeable in the sky. A UE-cell association is based on the strongest received signal power, i.e., each position is associated with the cell from which the strongest signal is received at that position. Figs. 2A-2D shows cell association patterns based on the strongest received power at heights of Om (ground level) , 50m, 100m, and 300m, respectively, in a simulated rural macro network. It can be seen that the cell association patterns change dramatically with height. The cell association pattern on the ground level is ideally a nicely defined and contiguous area where the best cell is most often the one closest to a UE. As the height increases, the antenna sidelobes start to be visible, and the best cell may no longer be the closest one to the UE. The cell association pattern in this particular scenario becomes fragmented especially at the height of 300m and above.

Fig. 3 shows an example of antenna sidelobes of base stations that could result in the scattered cell association as shown in Fig. 2D. As shown, a UE (e.g., UAV) 310 flies along a direction indicated by the horizontal arrow. Fig. 3 also shows a main lobe and a number of sidelobes of a base station 320, as well as sidelobes of

base stations

322, 324, and 326. It is assumed here that when the UAV 310 is in a coverage of both a sidelobe of the

base station

322, 324, or 326 and the main lobe of the base station 320, it receives a higher signal strength from the sidelobe than from the main lobe of the base station 320. In this case, the UE-cell association changes many times as the UAV 310 moves. As a result, the UAV 310 may execute handovers frequently. In a simulated scenario, a UAV flying at a speed of 160km/h at an altitude of 300m could execute more than 30 handovers within a range of 1500m, almost one handover every second in this case. The speed of 160km/h is a KPI requirement for the 4 ^th Generation (4G) network. The 5G network aims to support a UAV mobility up to 500km/h according to the 3 ^rd Generation Partnership Project (3GPP) Technical Report (TR) 38.913, V15.0.0, and in this case the handover performance could be even worse.

Moreover, the UAV 310 served by the sidelobes may experience very sharp drops, or nulls, in signal strengths when flying in the sky, e.g., at

positions

331, 333, and 335 shown in Fig. 3. At such positions, signal strengths drop rapidly, and a beam failure or Radio Link Failure (RLF) may occur before the UAV 310 can be handed over to another cell.

In most cases, a higher Handover Failure (HOF) rate and a higher RLF rate can be observed for aerial UEs. The HOF rate and the RLF rate become higher when the speed or the height of an aerial UE increases. For further information on the mobility performance of aerial UEs, reference can be made to 3GPP TR 36.777, V15.0.0, which is incorporated herein by reference in its entirety.

There is thus a need for a solution for improving the mobility performance of terminal devices (e.g., aerial UEs) out of the conventional terrestrial coverage.

SUMMARY

It is an object of the present disclosure to provide a method and a network device, capable of providing an enhanced coverage for a terminal device out of a conventional terrestrial coverage.

According to a first aspect of the present disclosure, a method in a network device is provided. The method includes: transmitting a Channel State Information -Reference Signal (CSI-RS) to a terminal device via a beam from a first set of candidate beams. The first set includes at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for Synchronization Signal and Physical Broadcast Channel ‘PBCH’ (SSB) transmission.

In an embodiment, the at least one candidate beam may have an elevation larger than any beam in the second set.

In an embodiment, the method may further include: detecting a beam failure or radio link failure associated with the terminal device; selecting one or more beams from a third set of candidate beams for SSB transmission, based on a beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and transmitting an SSB to the terminal device via each of the one or more beams.

In an embodiment, the beam failure or radio link failure may be detected in response to receiving an indication of the beam failure or radio link failure from the terminal device.

In an embodiment, the beam failure or radio link failure may be detected in response to determining one or more of: received power of a reference signal from the terminal device being lower than a threshold, or no Acknowledgement (ACK) or Non-Acknowledgement (NACK) having been received from the terminal device for a time period.

In an embodiment, the operation of selecting may include: determining a direction of the terminal device relative to the network device based on the beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and selecting, from the third set, the one or more beams to cover the direction.

In an embodiment, the method may further include: refraining from transmitting the SSB via each of the one or more beams in response to determining that the terminal device has recovered from the beam failure or radio link failure.

In an embodiment, the third set may include at least one candidate beam covering a spatial portion beyond the coverage of the second set.

In an embodiment, the at least one candidate beam included in the third set may have an elevation larger than any beam in the second set.

In an embodiment, the second set may be comprised of beams for always-on SSB transmission.

According to a second aspect of the present disclosure, a network device is provided. The network device includes a transceiver, a processor and a memory. The memory contains instructions executable by the processor whereby the network device is operative to perform the method according to the above first aspect.

According to a third aspect of the present disclosure, a computer readable storage medium is provided. The computer readable storage medium has computer program instructions stored thereon. The computer program instructions, when executed by a processor in a network device, cause the network device to perform the method according to the above first aspect.

With the embodiments of the present disclosure, the network device can transmit a CSI-RS to a terminal device via a beam covering a spatial portion beyond a coverage of a set of beams for SSB transmission. With such extended coverage, the terminal device is enabled to perform e.g., a cell search based on the CSI-RS when it is out of the coverage of SSBs transmitted by the network device, so as to provide improved mobility performance for the terminal device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:

Fig. 1 is a schematic diagram showing an exemplary scenario of LOS propagation for a UAV;

Figs. 2A-2D are schematic diagrams showing cell association patterns at different heights in a network;

Fig. 3 is a schematic diagram showing an example of antenna sidelobes of base stations;

Fig. 4 is a flowchart illustrating a method in a network device according to an embodiment of the present disclosure;

Fig. 5 is a schematic diagram showing an example of a CSI-RS beam space according to an embodiment of the present disclosure;

Fig. 6 is a schematic diagram showing an example of an extended SSB beam space according to an embodiment of the present disclosure;

Fig. 7 is a schematic diagram showing an exemplary time-domain configuration of an extended SSB beam space according to an embodiment of the present disclosure;

Fig. 8 is a schematic diagram showing an exemplary space-domain configuration of an extended SSB beam space according to an embodiment of the present disclosure;

Fig. 9 is a schematic diagram showing an exemplary scenario in which the present disclosure can be applied;

Fig. 10 is a block diagram of a network device according to an embodiment of the present disclosure;

Fig. 11 is a block diagram of a network device according to another embodiment of the present disclosure;

Fig. 12 schematically illustrates a telecommunication network connected via an intermediate network to a host computer;

Fig. 13 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and

Figs. 14 to 17 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

As used herein, the term "wireless communication network" refers to a network following any suitable communication standards, such as LTE-Advanced (LTE-A) , LTE, Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , and so on. Furthermore, the communications between a terminal device and a network device in the wireless communication network may be performed according to any suitable generation communication protocols, including, but not limited to, Global System for Mobile Communications (GSM) , Universal Mobile Telecommunications System (UMTS) , Long Term Evolution (LTE) , and/or other suitable 1G (the first generation) , 2G (the second generation) , 2.5G, 2.75G, 3G (the third generation) , 4G (the fourth generation) , 4.5G, 5G (the fifth generation) communication protocols, wireless local area network (WLAN) standards, such as the IEEE 802.11 standards; and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax) , Bluetooth, and/or ZigBee standards, and/or any other protocols either currently known or to be developed in the future.

The term "network device" refers to a device in a wireless communication network via which a terminal device accesses the network and receives services therefrom. The network device refers to a base station (BS) , an access point (AP) , or any other suitable device in the wireless communication network. The BS may be, for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , or a (next) generation NodeB (gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, a low power node such as a femto, a pico, and so forth. Yet further examples of the network device may include multi-standard radio (MSR) radio equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs) , base transceiver stations (BTSs) , transmission points, transmission nodes. More generally, however, the network device may represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a terminal device access to the wireless communication network or to provide some service to a terminal device that has accessed the wireless communication network.

The term "terminal device" refers to any end device that can access a wireless communication network and receive services therefrom. By way of example and not limitation, the terminal device refers to a mobile terminal, user equipment (UE) , or other suitable devices. The UE may be, for example, a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, portable computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable device, a personal digital assistant (PDA) , desktop computer, wearable terminal devices, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) and the like. In the following description, the terms "terminal device" , "terminal" , "user equipment" and "UE" may be used interchangeably. As one example, a terminal device may represent a UE configured for communication in accordance with one or more communication standards promulgated by the 3rd Generation Partnership Project (3GPP) , such as 3GPP′sGSM, UMTS, LTE, and/or 5G standards. As used herein, a "user equipment" or "UE" may not necessarily have a "user" in the sense of a human user who owns and/or operates the relevant device. In some embodiments, a terminal device may be configured to transmit and/or receive information without direct human interaction. For instance, a terminal device may be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the wireless communication network. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but that may not initially be associated with a specific human user.

The terminal device may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, and may in this case be referred to as a D2D communication device.

As yet another example, in an Internet of Things (IOT) scenario a terminal device may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another terminal device and/or network equipment. The terminal device may in this case be a machine-to-machine (M2M) device, which may in a 3GPP context be referred to as a machine-type communication (MTC) device. As one particular example, the terminal device may be a UE implementing the 3GPP narrow band internet of things (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances, for example refrigerators, televisions, personal wearables such as watches etc. In other scenarios, a terminal device may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation.

As still another example, a terminal device may be an aerial vehicle, such as a UAV, capable of communicating with a network device, or a UE in an aerial vehicle, e.g., a mobile phone carried by a passenger in a commercial airplane.

As used herein, a downlink, DL transmission refers to a transmission from the network device to a terminal device, and an uplink, UL transmission refers to a transmission in an opposite direction.

References in the specification to "one embodiment, " "an embodiment, " "an example embodiment, " and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a" , "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" , "comprising" , "has" , "having" , "includes" and/or "including" , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

In the 5G or New Radio (NR) network, a cell is defined by SSBs, and a coverage of a NR cell is determined by a coverage of the SSBs transmitted from a network device (also referred to as “SSB” coverage hereinafter) . The SSBs are typically transmitted in a “beam sweeping” manner, i.e., in different beams in a time division manner. The set of SSBs within a beam sweeping cycle is referred to as a Synchronization Signal (SS) burst set. Each SSB in the SS burst set has a time index that explicitly provides a relative location of the SSB within a sequence of possible SSB locations, and different SSB time indices correspond to SSB transmissions in different beam directions.

The SSBs are “always-on” signals in that they are always transmitted by a network device, regardless of user traffic. The always-on transmissions impose an upper limit on the achievable network energy performance and cause interference to other cells, thereby reducing the achievable data rates. In very dense networks deployed for high peak data rates, e.g., the 5G network, an average traffic load per network device can be expected to be relatively low, which makes the always-on signals a more substantial part of the overall transmissions in the network. Therefore, in the 5G network, an “ultra-lean” design principle is introduced, aiming at minimizing the always-on transmissions, thereby enabling higher network energy performance and higher achievable data rates. To follow the ultra-lean design principle, fewer SSBs are configured within a SS burst set to reduce resources allocated for SSB transmission. The maximum number (L) of SSBs per SS burst set is defined in 3GPP TS 38.213, V15.0.0, as shown in Table 1 below.

Table 1 -Maximum number (L) of SSBs per SS burst set

Carrier Frequency	Value of L
Below 3 GHz	4
Between 3&6 GHz	8
Between 6&52.6 GHz	64

In practice, a commercial base station may transmit much less SSBs per SS burst set than the maximum value of L. For example, a commercial base station may transmit only one SSB per SS burst set when L=8, or 12 SSBs per SS burst set when L=64.

Conventionally, for the purpose of terrestrial coverage, a coverage of beams for CSI-RS (and User Plane (UP) data) , also referred to as CSI-RS coverage, of a cell is always consistent with an SSB coverage of the cell. In other word, a network device does not transmit CSI-RS beams beyond its SSB coverage, as it would be meaningless for terrestrial UEs.

Typically, an aerial UE (e.g., a UAV) does not perform an initial access while it is in the sky. Instead, it performs the initial access to a cell on the ground, and then takes off for its flight mission. Accordingly, the UE can use the SSBs for initial cell search (initial access) while it is on the ground. In the sky, the UAV needs to remain connected for remote control and monitoring purposes, i.e., it does not enter the idle or inactive state. The UE in the connected state can perform a cell search for mobility management (e.g., beam switch or handover) based on either SSBs or CSI-RSs.

Fig. 4 is a flowchart illustrating a method 400 according to an embodiment of the present disclosure. The method 400 can be performed in a network device, e.g., an eNB or gNB.

At block 410, a CSI-RS is transmitted to a terminal device via a beam from a first set of candidate beams. Here, the terminal device can be an aerial UE, e.g., a UAV, or any other terminal device that may move out of a terrestrial coverage of the network device. The first set includes at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for SSB transmission. The first set can also be referred to as “CSI-RS beam space” hereinafter. The second set can be comprised of beams for always-on SSB transmission, i.e., for the terrestrial SSB coverage of the network device, and can also be referred to as “always-on SSB beam space” hereinafter.

In an example, the CSI-RS beam space may include at least one candidate beam having an elevation larger than any beam in the always-on SSB beam space. Fig. 5 shows an example of a CSI-RS beam space and an always-on SSB beam space. As shown, the CSI-RS beam space may be extended beyond the always-on SSB beam space, e.g., to include beams shown in dashed lines and covering higher elevations than the always-on SSB beam space, thereby providing an extended CSI-RS coverage in which CSI-RSs are transmitted to an aerial UE for cell search. In this way, the terminal device can perform cell search based on one or more CSI-RSs transmitted in the CSI-RS beam space even when it is out of the coverage of the always-on SSB beam space.

As discussed above, in a conventional scenario where the CSI-RS coverage is consistent with the (always-on) SSB coverage, the network device can use the same set of spatial filters (e.g., beamformers or precoding matrices) for CSI-RS transmission and SSB transmission. In order to implement the method 400, the network device may include one or more additional spatial filters for mapping one or more CSI-RSs to one or more directions that are not covered by the always-on SSB beam space. This can be achieved without any additional hardware cost.

The beam for CSI-RS transmission can also be used for transmission of UP data. With the extended coverage, the UP connection or service quality can also be improved accordingly.

When the quality of the connection between the terminal device and the network device becomes too low to maintain communication, a beam failure or RLF occurs and the terminal device loses its connection with the network device. In this case, the terminal device may need to reestablish the connection by means of random access, which requires an SSB from the network device. When the beam failure or RLF occurs when the terminal device is out of the coverage of the always-on SSB beam space, it may have to move into the coverage of the always-on SSB beam space for connection reestablishment.

In order to allow the terminal device to reestablish the connection while being out of the coverage of the always-on SSB beam space, upon detecting a beam failure or RLF associated with the terminal device, the network device can select one or more beams from a third set of candidate beams for SSB transmission, based on a beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected. Here, the third set can also be referred to as an “extended SSB beam space” . In particular, the network device can determine a direction of the terminal device relative to the network device based on the beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected, and select, from the extended SSB beam space, the one or more beams to cover the direction (usually an SSB beam is wider than a CSI-RS beam) . Then, the network device can transmit an SSB to the terminal device via each of the selected one or more beams.

In an example, the beam failure or radio link failure can be detected in response to determining one or more of: received power of a reference signal from the terminal device being lower than a threshold, or no ACK or NACK having been received from the terminal device for a time period.

The extended SSB beam space may include at least one candidate beam covering a spatial portion beyond the coverage of the second set. For example, the extended SSB beam space may include at least one candidate beam having an elevation larger than any beam in the second set. Fig. 6 shows an example of an extended SSB beam space. As shown, the extended SSB beam space may include beams shown in dashed lines and covering higher elevations than the always-on SSB beam space, thereby allowing the terminal device to reestablish the connection while being out of the coverage of the always-on SSB beam space, without having to move into the coverage of the always-on SSB beam space for recovery from the beam failure or RLF.

Following the “ultra-lean” design principle as discussed above, the SSB (s) in the extended SSB beam space may not be always-on. Thus, the network device can refrain from transmitting the SSB via each of the selected one or more beams in response to determining that the terminal device has recovered from the beam failure or radio link failure.

Fig. 7 shows an exemplary time-domain configuration of the extended SSB beam space. As discussed above, the number (denoted as N) of always-on SSBs transmitted per SS burst set may be smaller than the maximum allowable number L, i.e., N＜L. The extended SSB beam space may include a number, M, of candidate beams for SSB transmission. When a beam failure or RLF associated with a UE (e.g., a UAV) 710 occurs, a number, K, of SSBs (referred to as extended SSBs) can be transmitted to the UE 710 via K out of M beams in the extended SSB beam space in a beam-sweeping manner. Here, K≤M and K≤L-N.

Fig. 8 shows an exemplary space-domain configuration of the extended SSB beam space. As shown, N always-on SSBs cover an azimuth range from -60° to 60° and an elevation range from -30° to 0°. The extended SSB beam space may include M candidate beams for SSB transmission, covering an azimuth range from -60° to 60° and an elevation range from 0° to 90°. When a beam failure or RLF occurs, K extended SSBs can be transmitted via K out of M beams in the extended SSB beam space in a beam-sweeping manner. Again, K≤M and K≤L-N.

Fig. 9 is a schematic diagram showing an exemplary scenario in which the principles of the present disclosure can be applied. As shown, at Position PO, an aerial UE (e.g., UAV) 910 is in an idle state and receives a flight mission to Position P4 along a defined route. The UAV 910 performs initial access to a base station 920 based on always-on SSBs transmitted from the base station 920 in its always-on SSB beam space. Then, the UAV 910 enters a connected state and takes off and moves out of the coverage of the always-on SSB beam space at Position P1. From that on, the UAV 910 can be served by CSI-RS (UP data) beams (shown in dashed lines) transmitted from the base station 920 in its CSI-RS beam space. The UAV 910 can measure the CSI-RSs in the CSI-RS beam space for cell search (e.g., beam switch and handover) . At Position P2, the UAV 910 is handed over to a base station 922 and served by CSI-RS (UP data) beams (shown in dashed lines) transmitted from the base station 922 in its CSI-RS beam space. At Position P3, an RLF occurs and the UAV 910 loses its connection with the base station 922. The base station 922 detects the RLF, determines a direction of the UAV 910 relative to the base station 922 based on the beam used for CSI-RS transmission to the UAV 910 when or before the RLF occurs, selects an extended S5B beam from its extended SSB beam space and transmits an SSB to the UAV 910 via the selected extended SSB beam. Using the SSB, the UAV 910 can reestablish its connection with the base station 922. After that, the UAV 910 continues its flight, and is handed over to a base station 924 and then served by CSI-RS (UP data) beams (shown in dashed lines) transmitted from the base station 924 in its CSI-RS beam space, before it lowers its altitude and finally lands at Position P4.

Correspondingly to the method 400 as described above, a network device is provided. Fig. 10 is a block diagram of a network device 1000 according to an embodiment of the present disclosure.

The network device 1000 can be configured to perform the method 400 as described above in connection with Fig. 4. As shown in Fig. 10, the network device 1000 includes a transmitting unit 1010 configured to transmitting a CSI-RS to a terminal device via a beam from a first set of candidate beams. The first set includes at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for SSB transmission.

In an embodiment, the network device 1000 may further include: a detecting unit 1020 configured to detect a beam failure or radio link failure associated with the terminal device; and a selecting unit 1030 configured to select one or more beams from a third set of candidate beams for SSB transmission, based on a beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected. The transmitting unit 1010 can be further configured to transmit an SSB to the terminal device via each of the one or more beams.

In an embodiment, the detecting unit 1020 can be configured to detect the beam failure or radio link failure in response to receiving an indication of the beam failure or radio link failure from the terminal device.

In an embodiment, the detecting unit 1020 can be configured to detect the beam failure or radio link failure in response to determining one or more of: received power of a reference signal from the terminal device being lower than a threshold, or no ACK or NACK having been received from the terminal device for a time period.

In an embodiment, the selecting unit 1030 can be configured to: determine a direction of the terminal device relative to the network device based on the beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and select, from the third set, the one or more beams to cover the direction.

In an embodiment, the transmitting unit 1010 can be further configured to refrain from transmitting the SSB via each of the one or more beams in response to determining that the terminal device has recovered from the beam failure or radio link failure.

The above transmitting unit 1010, and optionally the detecting unit 1020 and the selecting unit 1030, can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro-processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component (s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in Fig. 4.

Fig. 11 is a block diagram of a network device 1100 according to another embodiment of the present disclosure.

The network device 1100 includes a transceiver 1110, a processor 1120 and a memory 1130. The memory 1130 can contain instructions executable by the processor 1120 whereby the network device 1100 is operative to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 4. Particularly, the memory 1130 can contain instructions executable by the processor 1120 whereby the network device 1100 is operative to: transmit a CSI-RS to a terminal device via a beam from a first set of candidate beams. The first set includes at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for SSB transmission.

In an embodiment, the memory 1130 may further contain instructions executable by the processor 1120 whereby the network device 1100 is operative to: detect a beam failure or radio link failure associated with the terminal device; select one or more beams from a third set of candidate beams for SSB transmission, based on a beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and transmit an SSB to the terminal device via each of the one or more beams.

In an embodiment, the beam failure or radio link failure may be detected in response to determining one or more of: received power of a reference signal from the terminal device being lower than a threshold, or no ACK or NACK having been received from the terminal device for a time period.

In an embodiment, the memory 1130 may further contain instructions executable by the processor 1120 whereby the network device 1100 is operative to: refrain from transmitting the SSB via each of the one or more beams in response to determining that the terminal device has recovered from the beam failure or radio link failure.

The present disclosure also provides at least one computer program product in the form of a non-volatile or volatile memory, e.g., a non-transitory computer readable storage medium, an Electrically Erasable Programmable Read-Only Memory (EEPROM) , a flash memory and a hard drive. The computer program product includes a computer program. The computer program includes: code/computer readable instructions, which when executed by the processor 1120 causes the network device 1100 to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 4.

The computer program product may be configured as a computer program code structured in computer program modules. The computer program modules could essentially perform the actions of the flow illustrated in Fig. 4.

The processor may be a single CPU (Central Processing Unit) , but could also comprise two or more processing units. For example, the processor may include general purpose microprocessors; instruction set processors and/or related chips sets and/or special purpose microprocessors such as Application Specific Integrated Circuits (ASICs) . The processor may also comprise board memory for caching purposes. The computer program may be carried by a computer program product connected to the processor. The computer program product may comprise a non-transitory computer readable storage medium on which the computer program is stored. For example, the computer program product may be a flash memory, a Random Access Memory (RAM) , a Read-Only Memory (ROM) , or an EEPROM, and the computer program modules described above could in alternative embodiments be distributed on different computer program products in the form of memories.

With reference to Fig. 12, in accordance with an embodiment, a communication system includes a telecommunication network 1210, such as a 3GPP-type cellular network, which comprises an access network 1211, such as a radio access network, and a core network 1214. The access network 1211 comprises a plurality of

base stations

1212a, 1212b, 1212c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a

corresponding coverage area

1213a, 1213b, 1213c. Each

base station

1212a, 1212b, 1212c is connectable to the core network 1214 over a wired or wireless connection 1215. A first UE 1291 located in a coverage area 1213c is configured to wirelessly connect to, or be paged by, the corresponding base station 1212c. A second UE 1292 in a coverage area 1213a is wirelessly connectable to the corresponding base station 1212a. While a plurality of

UEs

1291, 1292 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1212.

The telecommunication network 1210 is itself connected to a host computer 1230, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 1230 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider.

Connections

1221 and 1222 between the telecommunication network 1210 and the host computer 1230 may extend directly from the core network 1214 to the host computer 1230 or may go via an optional intermediate network 1220. An intermediate network 1220 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 1220, if any, may be a backbone network or the Internet; in particular, the intermediate network 1220 may comprise two or more sub-networks (not shown) .

The communication system of Fig. 12 as a whole enables connectivity between the connected

UEs

1291, 1292 and the host computer 1230. The connectivity may be described as an over-the-top (OTT) connection 1250. The host computer 1230 and the connected

UEs

1291, 1292 are configured to communicate data and/or signaling via the OTT connection 1250, using the access network 1211, the core network 1214, any intermediate network 1220 and possible further infrastructure (not shown) as intermediaries. The OTT connection 1250 may be transparent in the sense that the participating communication devices through which the OTT connection 1250 passes are unaware of routing of uplink and downlink communications. For example, the base station 1212 may not or need not be informed about the past routing of an incoming downlink communication with data originating from the host computer 1230 to be forwarded (e.g., handed over) to a connected UE 1291. Similarly, the base station 1212 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1291 towards the host computer 1230.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to Fig. 13. In a communication system 1300, a host computer 1310 comprises hardware 1315 including a communication interface 1316 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 1300. The host computer 1310 further comprises a processing circuitry 1318, which may have storage and/or processing capabilities. In particular, the processing circuitry 1318 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 1310 further comprises software 1311, which is stored in or accessible by the host computer 1310 and executable by the processing circuitry 1318. The software 1311 includes a host application 1312. The host application 1312 may be operable to provide a service to a remote user, such as UE 1330 connecting via an OTT connection 1350 terminating at the UE 1330 and the host computer 1310. In providing the service to the remote user, the host application 1312 may provide user data which is transmitted using the OTT connection 1350.

The communication system 1300 further includes a base station 1320 provided in a telecommunication system and comprising hardware 1325 enabling it to communicate with the host computer 1310 and with the UE 1330. The hardware 1325 may include a communication interface 1326 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 1300, as well as a radio interface 1327 for setting up and maintaining at least a wireless connection 1370 with the UE 1330 located in a coverage area (not shown in Fig. 13) served by the base station 1320. The communication interface 1326 may be configured to facilitate a connection 1360 to the host computer 1310. The connection 1360 may be direct or it may pass through a core network (not shown in Fig. 13) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 1325 of the base station 1320 further includes a processing circuitry 1328, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 1320 further has software 1321 stored internally or accessible via an external connection.

The communication system 1300 further includes the UE 1330 already referred to. Its hardware 1335 may include a radio interface 1337 configured to set up and maintain a wireless connection 1370 with a base station serving a coverage area in which the UE 1330 is currently located. The hardware 1335 of the UE 1330 further includes a processing circuitry 1338, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE 1330 further comprises software 1331, which is stored in or accessible by the UE 1330 and executable by the processing circuitry 1338. The software 1331 includes a client application 1332. The client application 1332 may be operable to provide a service to a human or non-human user via the UE 1330, with the support of the host computer 1310. In the host computer 1310, an executing host application 1312 may communicate with the executing client application 1332 via the OTT connection 1350 terminating at the UE 1330 and the host computer 1310. In providing the service to the user, the client application 1332 may receive request data from the host application 1312 and provide user data in response to the request data. The OTT connection 1350 may transfer both the request data and the user data. The client application 1332 may interact with the user to generate the user data that it provides.

It is noted that the host computer 1310, the base station 1320 and the UE 1330 illustrated in Fig. 13 may be similar or identical to the host computer 1930, one of base stations 1912a, 1912b, 1912c and one of UEs 1991, 1992 of Fig. 12, respectively. This is to say, the inner workings of these entities may be as shown in Fig. 13 and independently, the surrounding network topology may be that of Fig. 12.

In Fig. 13, the OTT connection 1350 has been drawn abstractly to illustrate the communication between the host computer 1310 and the UE 1330 via the base station 1320, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 1330 or from the service provider operating the host computer 1310, or both. While the OTT connection 1350 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network) .

Wireless connection 1370 between the UE 1330 and the base station 1320 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 1330 using the OTT connection 1350, in which the wireless connection 1370 forms the last segment. More precisely, the teachings of these embodiments may improve the data rate and latency, and thereby provide benefits such as reduced user waiting time.

A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1350 between the host computer 1310 and the UE 1330, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 1350 may be implemented in software 1311 and hardware 1315 of the host computer 1310 or in software 1331 and hardware 1335 of the UE 1330, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 1350 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which the

software

1311, 1331 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1350 may include message format, retransmission settings, preferred routing etc. ; the reconfiguring need not affect the base station 1320, and it may be unknown or imperceptible to the base station 1320. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer 1310’s measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the

software

1311 and 1331 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 1350 while it monitors propagation times, errors etc.

Fig. 14 is a flowchart illustrating a method implemented in a communication system, in accordance with an embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 12 and Fig. 13. For simplicity of the present disclosure, only drawing references to Fig. 14 will be included in this section. In step 1410, the host computer provides user data. In substep 1411 (which may be optional) of step 1410, the host computer provides the user data by executing a host application. In step 1420, the host computer initiates a transmission carrying the user data to the UE. In step 1430 (which may be optional) , the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1440 (which may also be optional) , the UE executes a client application associated with the host application executed by the host computer.

Fig. 15 is a flowchart illustrating a method implemented in a communication system, in accordance with an embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 12 and Fig. 13. For simplicity of the present disclosure, only drawing references to Fig. 15 will be included in this section. In step 1510 of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In step 1520, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1530 (which may be optional) , the UE receives the user data carried in the transmission.

Fig. 16 is a flowchart illustrating a method implemented in a communication system, in accordance with an embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 12 and Fig. 13. For simplicity of the present disclosure, only drawing references to Fig. 16 will be included in this section. In step 1610 (which may be optional) , the UE receives input data provided by the host computer. Additionally or alternatively, in step 1620, the UE provides user data. In substep 1621 (which may be optional) of step 1620, the UE provides the user data by executing a client application. In substep 1611 (which may be optional) of step 1610, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in substep 1630 (which may be optional) , transmission of the user data to the host computer. In step 1640 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

Fig. 17 is a flowchart illustrating a method implemented in a communication system, in accordance with an embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Fig. 12 and Fig. 13. For simplicity of the present disclosure, only drawing references to Fig. 17 will be included in this section. In step 1710 (which may be optional) , in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In step 1720 (which may be optional) , the base station initiates transmission of the received user data to the host computer. In step 1730 (which may be optional) , the host computer receives the user data carried in the transmission initiated by the base station.

The disclosure has been described above with reference to embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the disclosure. Therefore, the scope of the disclosure is not limited to the above particular embodiments but only defined by the claims as attached.

Claims

A method (400) in a network device, comprising:

transmitting (410) a Channel State Information -Reference Signal, CSI-RS, to a terminal device via a beam from a first set of candidate beams, the first set including at least one candidate beam covering a spatial portion beyond a coverage of a second set of beams for Synchronization Signal and Physical Broadcast Channel ‘PBCH’ , SSB, transmission.
The method (400) of claim 1, wherein the at least one candidate beam has an elevation larger than any beam in the second set.
The method (400) of claim 1 or 2, further comprising:

detecting a beam failure or radio link failure associated with the terminal device;

selecting one or more beams from a third set of candidate beams for SSB transmission, based on a beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and

transmitting an SSB to the terminal device via each of the one or more beams.
The method (400) of claim 3, wherein the beam failure or radio link failure is detected in response to receiving an indication of the beam failure or radio link failure from the terminal device.
The method (400) of claim 3, wherein the beam failure or radio link failure is detected in response to determining one or more of:

received power of a reference signal from the terminal device being lower than a threshold, or

no Acknowledgement, ACK, or Non-Acknowledgement, NACK, having been received from the terminal device for a time period.
The method (400) of any of claims 3-5, wherein said selecting comprises:

determining a direction of the terminal device relative to the network device based on the beam used for CSI-RS transmission to the terminal device when or before the beam failure or radio link failure is detected; and

selecting, from the third set, the one or more beams to cover the direction.
The method (400) of any of claims 3-6, further comprising:

refraining from transmitting the SSB via each of the one or more beams in response to determining that the terminal device has recovered from the beam failure or radio link failure.
The method (400) of any of claims 3-7, wherein the third set includes at least one candidate beam covering a spatial portion beyond the coverage of the second set.
The method (400) of claim 8, wherein the at least one candidate beam included in the third set has an elevation larger than any beam in the second set.
The method (400) of any of claims 1-9, wherein the second set is comprised of beams for always-on SSB transmission.
A network device (1100) , comprising a transceiver (1110) , a processor (1120) and a memory (1130) , the memory (1130) comprising instructions executable by the processor (1120) whereby the network device (1100) is operative to perform the method according to any of claims 1-10.
A computer readable storage medium having computer program instructions stored thereon, the computer program instructions, when executed by a processor in a network device, causing the network device to perform the method according to any of claims 1-10.