WO2019166099A1

WO2019166099A1 - Method, apparatus and computer program for random access procedure in a communication system

Info

Publication number: WO2019166099A1
Application number: PCT/EP2018/055139
Authority: WO
Inventors: Manasi Padhy
Original assignee: Nokia Technologies Oy
Priority date: 2018-03-02
Filing date: 2018-03-02
Publication date: 2019-09-06

Abstract

A method comprises receiving control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station and using said preamble in a random access procedure.

Description

METHOD, APPARATUS AND COMPUTER PROGRAM FOR RANDOM ACCESS

PROCEDURE IN A COMMUNICATION SYSTEM

Field of the disclosure

The present disclosure relates to methods, apparatuses and computer programs to perform, for example, a random access procedure in a communication system.

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/access points 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.

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) or user device. 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 or access point, 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. One example of a communications system is UTRAN (3G radio). 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. Another example communication system is so called 5G radio or NR (new radio) access technology.

Summary

According to an aspect there is provided a method comprising: receiving control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and using said preamble in a random access procedure. The method may be performed by a user equipment.

The method may comprise: receiving a plurality of beam reference signals from the base station, each beam reference signal being transmitted by the base station on a respective beam.

Each beam reference signal may be received from the base station in a sweeping subframe.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The method may comprise: determining beam state information for each beam reference signal received from the base station.

Beam state information may comprise beam reference signal received power. The method may comprise: causing the beam state information to be transmitted to the base station.

The method may comprise: causing respective beam state information to be transmitted to the base station with a respective beam index.

The control information may indicate a single preamble. The control information may be transmitted by the base station to the user equipment.

The single preamble may be uniquely allocated to the user equipment by the base station.

The control information may indicate a plurality of preambles mapped with a plurality of respective beam indexes in a mapping table.

Using said preamble in a random access procedure may comprise causing the preamble to be transmitted to the base station in a random access subframe.

Causing the preamble to be transmitted to the base station in a random access subframe may comprise causing the preamble to be transmitted to the base station in a random access subframe immediately following the subframe in which the control information is received from the base station.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided a method comprising: transmitting control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and using said preamble in a random access procedure. The method may be performed by a base station. The method may comprise: transmitting a plurality of beam reference signals to the user equipment, each beam reference signal being transmitted by the base station on a respective beam.

Each beam reference signal may be transmitted to the user equipment in a sweeping subframe.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The method may comprise: receiving beam state information from the user equipment for each beam reference signal.

The beam state information may comprise receiving beam reference signal received power.

The method may comprise: receiving beam state information from the user equipment for each beam reference signal with a respective beam index.

The control information may comprise a plurality of preambles mapped with a respective beam of the plurality of beams in a mapping table.

Using said preamble in a random access procedure may comprise receiving the preamble from the user equipment in a random access subframe. Receiving the preamble from the user equipment in a random access subframe may comprise receiving the preamble from the user equipment in a random access subframe immediately following a subframe in which the control information is transmitted by the base station.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided an apparatus comprising: means for receiving control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and means for using said preamble in a random access procedure. The apparatus may be a user equipment.

The apparatus may comprise: means for receiving a plurality of beam reference signals from the base station, each beam reference signal being transmitted by the base station on a respective beam.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The apparatus may comprise: means for determining beam state information for each beam reference signal received from the base station.

Beam state information may comprise beam reference signal received power.

The apparatus may comprise: means for causing the beam state information to be transmitted to the base station. The apparatus may comprise: means for causing respective beam state information to be transmitted to the base station with a respective beam index.

Means for using said preamble in a random access procedure may comprise means for causing the preamble to be transmitted to the base station in a random access subframe.

Means for causing the preamble to be transmitted to the base station in a random access subframe may comprise means for causing the preamble to be transmitted to the base station in a random access subframe immediately following the subframe in which the control information is received from the base station.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided an apparatus comprising: means for transmitting control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and means for using said preamble in a random access procedure. The apparatus may be a base station. The apparatus may comprise: means for transmitting a plurality of beam reference signals to the user equipment, each beam reference signal being transmitted by the base station on a respective beam.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The apparatus may comprise: means for receiving beam state information from the user equipment for each beam reference signal.

The apparatus may comprise: means for receiving beam state information from the user equipment for each beam reference signal with a respective beam index.

Means for using said preamble in a random access procedure may comprise means for receiving the preamble from the user equipment in a random access subframe. Means for receiving the preamble from the user equipment in a random access subframe may comprise means for receiving the preamble from the user equipment in a random access subframe immediately following a subframe in which the control information is transmitted by the base station.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided an apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: receive control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and use said preamble in a random access procedure. The apparatus may be a user equipment.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: receive a plurality of beam reference signals from the base station, each beam reference signal being transmitted by the base station on a respective beam.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: determine beam state information for each beam reference signal received from the base station.

Beam state information may comprise beam reference signal received power. The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: cause respective beam state information to be transmitted to the base station.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: cause each beam state information to be transmitted to the base station with a respective beam index.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided an apparatus comprising at least one processor and at least one memory including computer code for one or more programs, the at least one memory and the computer code configured, with the at least one processor, to cause the apparatus at least to: transmit control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and use said preamble in a random access procedure. The apparatus may be a base station.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: transmit a plurality of beam reference signals to the user equipment, each beam reference signal being transmitted by the base station on a respective beam.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: receive beam state information from the user equipment for each beam reference signal.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: receive beam state information from the user equipment for each beam reference signal with a respective beam index.

The control information may indicate a single preamble. The control information may be transmitted by the base station to the user equipment. The single preamble may be uniquely allocated to the user equipment by the base station.

Using said preamble in a random access procedure may comprise receiving the preamble from the user equipment in a random access subframe.

Receiving the preamble from the user equipment in a random access subframe may comprise receiving the preamble from the user equipment in a random access subframe immediately following a subframe in which the control information is transmitted by the base station.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

According to an aspect there is provided a computer program comprising computer executable code which when run on at least one process is configured to: receive control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and use said preamble in a random access procedure. The computer program may be executed by a user equipment.

The at least one process may be configured to: receive a plurality of beam reference signals from the base station, each beam reference signal being transmitted by the base station on a respective beam.

Each beam reference signal may be received from the base station in a sweeping subframe. The sweeping subframe may have a subframe index of Ό’ or‘25’.

The at least one process may be configured to: determine beam state information for each beam reference signal received from the base station.

Beam state information may comprise beam reference signal received power.

The at least one process may be configured to: cause the beam state information to be transmitted to the base station.

The at least one memory and the computer code may be configured, with the at least one processor, to cause the apparatus to: cause respective beam state information to be transmitted to the base station with a respective beam index.

The random access subframe may have a subframe index of Ί 5’ or‘40’. According to an aspect there is provided a computer program comprising computer executable code which when run on at least one process is configured to: transmit control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and use said preamble in a random access procedure. The computer program may be executed by a base station.

The at least one process may be configured to: transmit a plurality of beam reference signals to the user equipment, each beam reference signal being transmitted by the base station on a respective beam.

The sweeping subframe may have a subframe index of Ό’ or‘25’.

The at least one process may be configured to: receive beam state information from the user equipment for each beam reference signal.

The at least one process may be configured to: receive beam state information from the user equipment for each beam reference signal with a respective beam index.

The random access subframe may have a subframe index of Ί 5’ or‘40’.

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

According to an aspect, there is provided a computer readable medium comprising program instructions stored thereon for performing at least one of the above methods. The computer readable medium may be comprised in a user equipment or a base station.

According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least one of the above methods. The non-transitory computer readable medium may be comprised in a user equipment or a base station.

Various other aspects are also described in the following detailed description and in the attached claims. Brief

of the

Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

Figure 1 shows a schematic representation of a control apparatus according to some embodiments;

Figure 2 shows a schematic representation of a communication device;

Figure 3 shows a schematic representation of a frame;

Figure 4 shows a schematic representation of a subframe;

Figure 5 shows a schematic representation of a slot;

Figure 6 shows a schematic representation of beamforming reference signal symbols;

Figure 7 shows a schematic representation of random access channel symbols;

Figure 8 shows a schematic representation of consecutive frames;

Figure 9 shows method steps performs by a base station and a user equipment in an embodiment;

Figure 10 shows method steps performs by a base station and a user equipment in another embodiment; and

Figure 11 shows a schematic representation of consecutive frames. Detailed Description of the Figures

In the following certain exemplifying embodiments are explained with reference to mobile communication devices capable of communication via a wireless cellular system and mobile communication systems serving such mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1 and 2 to assist in understanding the technology underlying the described examples.

A communication device 20 or terminal such as shown in Figure 2 can be provided wireless access via base stations or similar wireless transmitter and/or receiver nodes providing access points of a radio access system.

An access point, for example a base station, may provide at least one antenna beam directed in the direction of the communication device 20 at a given time. In some embodiments a plurality of beams may be directed at a communication device from one or more access points. The antenna beam can be provided by appropriate elements of antenna arrays of the access points. For example, access links between the access points (AP) and a user equipment (UE) can be provided by active antenna arrays. Such arrays can dynamically form and steer narrow transmission/reception beams and thus serve UEs and track their positions. This is known as user equipment-specific beamforming. The active antenna arrays can be used both at the access point and at the user device to further enhance the beamforming potential. More than one beam can be provided by each access point and/or antenna array.

Access points and hence communications there through are typically controlled by at least one appropriate controller apparatus so as to enable operation thereof and management of mobile communication devices in communication therewith. Figure 1 shows an example of a control apparatus for a node, for example to be integrated with, coupled to and/or otherwise for controlling the access points. The control apparatus 10 can be arranged to provide control on communications via antenna beams by the access points and on operations such as handovers between the access points. For this purpose the control apparatus comprises at least one memory 11 , at least one data processing unit 12, 13 and an input/output interface 14. Via the interface the control apparatus can be coupled to relevant other components of the access point. The control apparatus can be configured to execute an appropriate software code to provide the control functions. It shall be appreciated that similar components can be provided in a control apparatus provided elsewhere in the network system, for example in a core network entity. The control apparatus can be interconnected with other control entities. The control apparatus and functions may be distributed between several control units. In some embodiments, each base station can comprise a control apparatus. In alternative embodiments, two or more base stations may share a control apparatus.

Access points and associated controllers may communicate with each other via a fixed line connection and/or via a radio interface. The logical connection between the base station nodes can be provided for example by an X2 or the like interface. This interface can be used for example for coordination of operation of the stations.

The communication device or user equipment (UE) 20 may comprise any suitable device capable of at least receiving wireless communication of data. For example, the device can be handheld data processing device equipped with radio receiver, data processing and user interface apparatus. Non-limiting examples include a mobile station (MS) such as a mobile phone or what is known as a’smart phone’, a portable computer such as a laptop or a tablet computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. Further examples include wearable wireless devices such as those integrated with watches or smart watches, eyewear, helmets, hats, clothing, ear pieces with wireless connectivity, jewellery and so on, universal serial bus (USB) sticks with wireless capabilities, modem data cards, machine type devices or any combinations of these or the like.

Figure 2 shows a schematic, partially sectioned view of a possible communication device. More particularly, a handheld or otherwise mobile communication device (or user equipment UE) 20 is shown. A mobile communication device is provided with wireless communication capabilities and appropriate electronic control apparatus for enabling operation thereof. Thus the communication device 20 is shown being provided with at least one data processing entity 26, for example a central processing unit and/or a core processor, at least one memory 28 and other possible components such as additional processors 25 and memories 29 for use in software and hardware aided execution of tasks it is designed to perform. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board 27 and/or in chipsets. Data processing and memory functions provided by the control apparatus of the communication device are configured to cause control and signalling operations in accordance with certain embodiments as described later in this description. A user may control the operation of the communication device by means of a suitable user interface such as touch sensitive display screen or pad 24 and/or a key pad, one of more actuator buttons 22, voice commands, combinations of these or the like. A speaker and a microphone are also typically 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 device may communicate wirelessly via appropriate apparatus for receiving and transmitting signals. Figure 2 shows schematically a radio block 23 connected to the control apparatus of the device. The radio block can comprise a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the communication device. The antenna arrangement may comprise elements capable of beamforming operations. Some embodiments relate to mobile communication networks with beamforming techniques. For example, 5G radio access technology and LTE-A (Long term evolution - advanced) evolution have proposed using beamforming techniques. It should be appreciated that other embodiments may be used with any other communication system or standard which uses beamforming. For example some wireless area networks may use beamforming.

The 5G radio system may use frequencies from 400MHz to 100GHz. Beamforming is considered to be desirable in enabling the use of the higher frequency bands due to coverage issues. It should be appreciated, that other embodiments may use different frequency ranges.

Some transceivers (e.g. a hybrid transceiver architecture) may use analogue beamforming, which may mean a large amount of narrow beams as this is dependent on the number of antenna elements and carrier frequency. It should be appreciated that other embodiments may be used with digital beamforming transceiver architecture or so-called hybrid transceiver architecture which use a hybrid of digital baseband processing (such as MIMO multiple input multiple output and /or digital precoding) and analogue beamforming. It should be appreciated that embodiments can be used with any method of beamforming.

To compensate the increased path loss when operating on higher frequencies, beamforming has been proposed to provide efficient 5G cell coverage. The aforementioned transceiver architectures implement beam forming. As an example, systems deployed to lower frequencies (~sub 6 GHz) may be implemented by using fully digital architecture, and the higher frequencies where the number of antenna elements required for cell coverage may range from tens to hundreds may be implemented by using a hybrid-architecture, or even a fully analogue architecture.

Relatively large antenna array gains, at both the access point, (e.g. 18 dB with 64 antenna elements) and the user device (e.g. 9dB with 8 antenna elements) may be achieved to compensate propagation loss and/or losses for example due to rain and oxygen absorption. Different embodiments may of course operate at different carrier frequencies and/or with different numbers of antenna elements.

Some embodiments may use a carrier frequency of 28GHz and a system bandwidth of 100MHz. However, this is by way of example only and different carrier frequencies and/or bandwidths may be used in other embodiments.

Figures 3 to 5 show schematically the structure of a radio frame of a 5G radio system. The radio frame is typically identified by a system frame index SF0 to SFN. The radio frame has a time period of 1536000T_S which may be 10 ms. T_s represents an achievable data rate period that can handle the 5G radio system for a binary modulation. The radio frame comprises fifty subframes. Each subframe is identified by a subframe index sfO to sf49. Each subframe has a time period of 30720T_S or 0.2 ms. Each subframe comprises two slots. Each slot is identified by a slot index slotO to slot99. Each slot has a time period of 15360T_S or 0.1 ms. Each slot comprises seven Orthogonal Frequency Division Multiplexing (OFDM) symbols.

Subframes may be reserved for broadcasting a primary synchronization signal (PSS), a secondary synchronization signal (SSS), an extended synchronization signal (ESS), beam reference signal (BRS) and physical broadcast channel (xPBCH) in the downlink. Subframes reserved for broadcasting the BRS are sometimes referred to as scanning subframes or sweeping subframes.

In an example, both subframes sfO and sf025 are reserved for broadcasting a primary synchronization signal (PSS), a secondary synchronization signal (SSS), an extended synchronization signal (ESS), beam reference signal (BRS) and physical broadcast channel (xPBCH) in the downlink.

The purpose of the PSS, SSS and ESS is to synchronise a user equipment with a base station. PSS occupies sixty two subcarriers. PSS is allocated seventy two subcarriers (i.e. six resource blocks of twelve subcarriers each) so that five subcarriers on each side of PSS are left unused and form a gap. SSS occupies sixty two subcarriers. SSS is allocated seventy two subcarriers (i.e. six resource blocks of twelve subcarriers each) so that five subcarriers on each side of SSS are left unused and form a gap. ESS occupies sixty two subcarriers. ESS is allocated seventy two subcarriers (i.e. six resource blocks of twelve subcarriers each) so that five subcarriers on each side of PSS are left unused and form a gap.

The purpose of BRS is to allow a user equipment to assess the quality of each beam of a base station. BRS is allocated two groups of three hundred and twenty eight subcarriers each (i.e. each group comprises forty one resource blocks of eight subcarriers each).

The maximum number of BRS transmissions may depend on the BRS configuration. For example, the BRS configuration may be as defined in“v5G.211 Table 6.7.4.3-1 : Logical beam index mapping according to BRS transmission period” (reproduced below).

In an example, the BRS transmission period is 10 ms, the total number of antenna ports P is one and the number of symbols per slot is seven. Accordingly, the maximum number of beams trained by the base station and therefore the maximum number of BRS transmitted by the base station is equal to twenty eight. The purpose of xPBCH may be to carry master information blocks (MIB).

BRS is allocated two groups of one hundred and sixty four subcarriers each (i.e. each group comprises forty one resource blocks of four subcarriers each). The resource blocks allocated to the xPBCH are interleaved with the resource blocks allocated to the BRS.

Subframes may also be reserved for a physical random access channel (xPRACH). The purpose of xPRACH is to allow a user equipment to transmit a RACH preamble to the base station to perform an initial access procedure. These subframes are also called RACH subframes.

The number of subframes reserved for the xPRACH may depend on the PRACH configuration. For example, reference is made to the table below, as defined in“v5G.211 Table 5.7.1 -2: Random access configuration”.

In an example, both subframes sf15 and sf40 are reserved for xPRACH.

In an example, subframes sf1 to sf14, sf16 to sf24, sf26 to sf39 and sf41 to sf49 may be used for data.

Figure 6 shows how BRS symbols are transmitted in subframes sfO and sf25. As explained above, each subframe sfO and sf25 comprises two slots of seven symbols each. That is, each subframe sfO and sf25 comprises fourteen opportunities to transmit a BRS. In each symbol, a base station may transmit a BRS symbol for a respective beam. Each beam is associated with a respective direction. Each beam is identified by a beam index (Bl) of BIO to BI27 (e.g. twenty eight beam opportunities are possible).

Beam state information may be determined by a user equipment for each beam based on the BRS symbols. For example, the user equipment may receive each BRS symbol, determine a beam reference signal received power (BRSRP) for each beam based on the BRS symbols, and report the BRSRP and Bl for each beam to the base station.

In this way, the base station can determine a preferred beam or beams to align the user equipment and the base station. The preferred beam may be the beam with the highest BSRP. In an example, the preferred beam is identified by BI17.

Figure 7 shows how RACH symbols are transmitted in subframes sf15 and sf40 in more detail. As explained above, each subframe sf15 and sf40 may comprise two slots of seven symbols each. RACH symbols are not aligned with these symbols. That is, the number of RACH symbols transmitted in each slot is different than seven.

A RACH symbol is composed of two instances of a random access preamble. The random access preamble comprises a cyclic prefix (CP) and a sequence (SEQ). The cyclic prefix (CP) and sequence (SEQ) may be generated from a Zadoff-Chu sequence or similar sequence.

The number of RACH symbols transmitted per subframe depends on the preamble format. This may be as defined in“v5G.211 Table 5.7.1 -1 : Random access preamble parameters” (reproduced below).

In preamble format 0, the number of RACH symbols transmitted per subframe is five. This format is typically used for a cell radius of 500m.

In preamble format 1 , the number of RACH symbols transmitted per subframe is four. This format is typically used for a cell radius of 1 km. In an example, the preamble format Ό’ is used but it will be understood that preamble format Ί’ could equally be used.

After aligning the base station and the user equipment, the user equipment selects a random access preamble, computes a RACH symbol based on the random access preamble and determines on which RACH subframe to transmit the RACH symbol to the base station.

It has been proposed to configure the user equipment to determine a set of Bis associated with each RACH subframe of each frame. This may be based on the equation set out in“v5G.211 section 5.7.2.1” (reproduced below).

where:

M is the number of RACH subframes per frame. M is set to one if the PRACH configuration is Ό’ and set to two if the PRACH configuration is Ύ.

SFN is the index of the frame.

NRACH is the number of symbols during each RACH subframe for which the base station applies different reception beam. NRACH is set to five if the preamble format is Ό’ and set to four if the preamble format is set to Ί’. m is an index of the RACH subframe within the frame m is set to Ό’ for a subframe sf15. m is set to Ί’ for a subframe sf40.

NBRS is the number of BRS transmission periods (in slots) multiplied by seven. % is the modulo operator.

Once, a user equipment has determined the set of Bis associated with a RACH subframe of a frame, the user equipment determines whether the Bl of the preferred beam is within the set of Bis. If this is the case, the user equipment can transmit a RACH symbol in the subframe. Otherwise, the user equipment determines a set of Bis associated with another RACH subframe.

Figure 8 shows an example where the preferred beam is BI17. The user equipment determines the set of Bis associated with each subframe sf15 and sf40 of each frame SFN1 to SFN4. The user equipment may obtain the following results.

Based on these results, the user equipment may determine that the RACH symbol may be transmitted in subframe sf40 of SFN1 or in sf40 of SFN4.

Such technique for initiating a random access procedure may have some issue in some scenarios. For example, the delay between the initiation of the beam alignment procedure (or synchronization procedure) and the initiation of the random access procedure is often too long. For example, as can be seen in Figure 8, the delay between the reception of the BRS symbol for the beam Bl 17 in the subframe sf25 of the frame SFN 2 by the user equipment and the transmission of the RACH symbol in RACH subframe sf40 of frame SFN4 by the user equipment may be too long. Moreover, the completion of the random access procedure is not always successful because several user equipment may align with the same base station along the same beam, may select the same random access preamble and may transmit the same random access preamble on the same RACH subframe. Accordingly, there may be a collision (or contention), the resolution of which is not always possible and if possible delays the completion of the random access procedure.

The initial access to the radio network for the user equipment may be crucial and complex in 5G new radio due to multi beam approach. The user equipment has to synchronize to the best beam and initiate RACH to the best beam very frequently due to the challenges in thin beam coverage and also blocking and rotation issue that leads to dynamic point selection of the beams. The dynamic point selection to the beams has to be quick so as to address the 5G requirements of coverage and low latency. However the RACH subframes use the same beams as the synchronization subframes and in the same sequential order hence there is significant delay between user equipment synchronizing to the best beam and doing RACH to it for the initial access. Also there could be possibility that if RACH procedure gets unsuccessful then it has to retry the RACH in the RACH subframe as defined in the specification“V5G_211_v1 p7 Clause 5.7.2”. Every time the delay between the synchronization and RACH process will be more when the RACH preamble mapped to the best beam index

is corresponding to the Nth RACH subframe of the radio frame SFN1 , SFN2, SFN4 and SFN8.

Figure 9 shows schematically a flow diagram of a method according to an embodiment. The method is performed by a base station and a user equipment. For example, the base station is a 5G base station (e.g. gNB) and the user equipment is a 5G user equipment. The base station comprises a layer 1 entity or PHYsical entity (PHY). The base station also comprises a layer 2 entity of medium access control entity (MAC).

In step 101 , the PHY entity of the base station transmits a plurality of BRS to the user equipment for a plurality of respective beams in a sweeping subframe. The transmission may be performed by one or more downlink instances of the PHY entity of the base station.

For example, the PHY entity of the base station transmits BRS symbols for beams BIO to BI13 in subframes sfO of each frame and BRS symbols for beams BI14 to BI27 in subframes sf25 of each frame as shown in Figure 6.

In step 102, the user equipment receives the BRS from the base station for each beam in the sweeping subframes. The user equipment then determines beam state information for each beam.

For example, the user equipment receives BRS symbols for beams BIO to BI13 in subframe sfO of frame SF2 and receives BRS symbols for beams BI14to BI27 in subframe sf25 of frame SF2. The user equipment determines BRSRP1 to BRSRP13 for beams BIO to BI13. The user equipment determines BRSRP14 to BRSRP27 for beams BI14 to BI27.

In step 103, the user equipment transmits the beam state information for each beam to the PHY entity of the base station. The transmission may be performed via a Physical Uplink Control Channel (xPUCCH) or a Physical Uplink Shared Channel (xPUSCH).

For example, the user equipment transmits the BRSRP1 to BRSRP27 with their respective beam indexes BI1 to BI27 to the PHY entity of the base station in subframe sf29 of frame SF2. In step 104, the PHY entity of the base station receives the beam state information for each beam and transmits the beam state information for each beam to of the MAC entity of the base station. The reception/ transmission may be performed by one or more uplink instances of the PHY entity of the base station. The transmission may be performed to a scheduler of the MAC entity of the base station.

For example, the PHY entity of the base station receives BRSRP1 to BRSRP27 with the respective beam index BI1 to BI27 and transmits the BRSRP1 to BRSRP27 with the respective beam index BI1 to BI27 to the MAC entity of the base station.

In step 105, the MAC entity of the base station processes the beam state information for each beam. The MAC entity of the base station determines a beam (i.e. preferred beam) to align for communication with the user equipment. The MAC entity of the base station determines whether a change of beam to be used by a user equipment for communication with the base station is needed. The processing may be performed by a beam tracking function of the MAC entity of the base station.

For example, the MAC entity of the base station processes the BRSRP1 to BRSRP27 with the respective beam index BI1 to BI27 and determines that the beam index BI17 is associated with the highest BRSRP. The beam with BI17 is the preferred beam and is to be used by the user equipment for communication with the base station.

In step 106, the MAC entity of the base station selects a random access preamble. As discussed above, the random access preamble may be generated based on a Zadoff Chu sequence or similar sequence. The random access preamble may be unique to the user equipment. The MAC entity then transmits a beam change indication (BCI) to the user equipment. The BCI comprises the beam to be used by the user equipment for communication with the base station and the selected random access preamble. The BCI may be transmitted on a transport channel such as a downlink shared channel (DL-SCH). The BCI may be transmitted on a physical channel such as a physical downlink control channel (PDCCH) or a physical downlink shared channel (PDSCH). The BCI may be transmitted in a subframe following the subframe in which the user equipment transmits the beam state information. For example, the BCI may be transmitted in the subframe immediately following the subframe in which the user equipment transmits the beam state information.

For example, the MAC entity transmits a BCI to the user equipment comprising the beam index BI17 and the selected random access preamble in subframe sf33 of frame SF2.

In step 107, the user equipment receives the BCI. The user equipment aligns the user equipment with the base station along the beam indicated by the BCI. Then, the user equipment initiates the random access procedure. The user equipment generates a RACFI symbol based on the random access preamble indicated by the BCI. The user equipment transmits the RACFI symbol in a RACFI subframe following the subframe in which the user equipment received the BCI. In some embodiments, the user equipment transmits the RACFI symbol in the RACFI subframe immediately following the subframe in which the user equipment received the BCI.

For example, the user equipment receives the BCI in subframe sf33 of frame SFN 2. The user equipment aligns with the base station along the beam with BI17. The user equipment generates a RACFI symbol based on the random access preamble indicated in the BCI. The user equipment transmits the RACFI symbol in the RACFI subframe sf40 of frame SFN2.

In some embodiments, an advantage of the method of figure 9 over existing methods is that the time period between the initiation of the beam alignment procedure and the initiation of the random access procedure may be reduced. For example, as can be seen in Figure 11 , the time period between the reception of the BRS symbol for the beam BI17 in the subframe sf25 of the frame SFN 2 by the user equipment and the transmission of the RACH symbol in RACH subframe sf40 of frame SFN2 by the user equipment is shorter. In this way, the completion of the random access procedure may be quicker, which is particularly useful when frequent beam update are needed (e.g. in case of cm and mm wave 5G radio systems).

Moreover, because the random access preamble is selected by the MAC entity of the base station and may be unique to the user equipment, the random access procedure may be contention free and the random access procedure is more likely to be successful.

Figure 10 shows schematically a flow diagram of a method according to another embodiment. The method of Figure 10 may identical to the method of Figure 9 except that steps 106 and 107 may be replaced by steps 206, 207 and 208.

In step 206, the MAC entity of the base station transmits a BCI to the user equipment. The BCI comprises the beam to be used by a user equipment for communication with the base station and may or may not comprise a selected random access preamble. Also in step 206 the user equipment receives the BCI and aligns the user equipment with the base station along the beam indicated in the BCI. The BCI may be transmitted on a transport channel such as a downlink shared channel (DL-SCFI). The BCI may further be transmitted on a physical channel such as a physical downlink control channel (PDCCFI) or a physical downlink shared channel (PDSCFI). The BCI may be transmitted in a subframe following the subframe in which the user equipment transmits the beam state information. For example, the BCI may be transmitted in the subframe immediately following the subframe in which the user equipment transmits the beam state information.

For example, the user equipment receives the BCI comprising BI17 in subframe sf33 of frame SFN 2 and aligns the user equipment with the base station along the beam associated with the BI17. In step 207, the MAC entity of the base station selects a plurality of random access preambles. As discussed above, each random access preamble may be generated based on a Zadoff Chu sequence or similar sequence. The plurality of random access preambles may not be unique to the user equipment. The MAC entity of the base station maps the plurality of random access preambles to a plurality of respective beam indexes in a mapping table. The MAC entity of the base station then transmits the mapping table to the user equipment. The transmission may be performed in a MAC control element in downlink control information (DCI). Also in step 207, the user equipment receives the mapping table. The DCI may be transmitted on a transport channel such as a downlink shared channel (DL-SCH). The DCI may further be transmitted on a physical channel such as a physical downlink control channel (PDCCH) or a physical downlink shared channel (PDSCH). The DCI may be transmitted in the same subframe as the BCI or in a separate subframe than the BCI. In an implementation, the DCI may be transmitted in a subframe following the subframe in which the BCI is transmitted.

For example, the MAC entity of the base station selects fourteen random access preambles and map the fourteen random access preambles to beam indexes BIO to BI13 in a mapping table and then transmits the mapping table to the user equipment in subframe sf37 of frame SFN 2.

In step 208, the user equipment determines which random access preamble is to be used by the user equipment to initiate a random access procedure with the base station based on the beam indicated in the BCI (in step 206) and the mapping table received in the DCI (in step 207).

For example, the user equipment receives the beam index BI17 in the BCI and determines which random access preamble is mapped to the beam index BI17 in the mapping table in the DCI.

Also in step 208, the user equipment initiates the random access procedure.

The user equipment generates a RACFI symbol based on the determined random access preamble (in step 207). The user equipment transmits the RACH symbol in a RACH subframe following the subframe in which the user equipment received the latest of the BCI and DCI. In some embodiment, the user equipment transmits the RACH symbol in the RACH subframe immediately following the subframe in which the user equipment received the latest of the BCI and the DCI.

For example, the user equipment receives the BCI in subframe sf33 of frame SFN2. The user equipment receives the DCI in subframe sf33 or sf37 of frame SFN2. It will be understood that the DCI is transmitted in the subframe sf33 if it is to be transmitted along with BCI message else DCI is transmitted in sf37. The user equipment transmits the RACH symbol in the RACH subframe sf40 of frame SFN2. It will be understood that the user equipment may transmit the RACH symbol if the base station can successfully transmit the DCI with the preamble information before the RACH subframe occurance. It will be understood that subframes sf33 or sf37 are downlink subframes and the indexes of downlink subframes depend on the frame configuation. In other configurations, dowlink subframes may have indexes different than sf33 and sf37.

In some embodiments, an advantage of the method of Figure 10 over existing methods is that the time period between the initiation of the beam alignment procedure and the initiation of the random access procedure may be reduced. In this way, the completion of the random access procedure will be accelerated, which is particularly useful when frequent beam update are needed (e.g. in case of cm and mm wave 5G radio systems).

Moreover, traffic overhead between the base station and the user equipment may be reduced because the base station does not have to transmit a random access preamble to the user equipment every time the base station transmits a Beam Change Indication. The user equipment may use the mapping table.

However, in some embodiments the completion of the random access procedure may not always be successful. Indeed, several user equipment may align with the same base station along the same beam, may receive the same mapping table from the base station, may select the same random access preamble in the mapping table, and may transmit the same RACH symbol on the same RACH subframe. Accordingly, the method of Figure 10 may not be contention free as opposed to the method of Figure 9.

It will be understood that although the above embodiments have been described in the context of 5G, other embodiment could be implement in other types of radio access networks.

It will also be understood that in the indexes of subframes and frames in the above example to transmit the BRS, the BRSRP, the BCI and/or the DCI is purely illustrative and other indexes of subframes and frames may be used depending on the uplink and downlink configuration of the subframes within the frames.

The required data processing apparatus and functions may be provided by means of one or more data processors. The apparatus may be provided in the communications device, in the control apparatus and/or in the access point. The described functions at each end may be provided by separate processors or by an integrated processor. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non-limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories 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. 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 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 foregoing description has provided by way of exemplary and 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 spirit and scope of this invention as defined in the appended claims. Indeed there is a further embodiment comprising a combination of one or more of any of the other embodiments previously discussed.

Claims

1. A method comprising:

receiving control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

using said preamble in a random access procedure.

2. A method as claimed in claim 1 , comprising:

receiving a plurality of beam reference signals from the base station, each beam reference signal being transmitted by the base station on a respective beam.

3. A method as claimed in claim 2, wherein each beam reference signal is received from the base station in a sweeping subframe.

4. A method as claimed in claim 3, wherein the sweeping subframe has a subframe index of Ό’ or‘25’.

5. A method as claimed in any of claims 2 to 4, comprising:

determining beam state information for each beam reference signal received from the base station.

6. A method as claimed in claim 5, wherein beam state information comprises beam reference signal received power.

7. A method as claimed in any of claims 5 or 6, comprising:

causing the beam state information to be transmitted to the base station.

8. A method as claimed in claim 7, comprising:

causing respective beam state information to be transmitted to the base station with a respective beam index.

9. A method as claimed on any of claims 1 to 8, wherein the control information indicates a single preamble.

10. A method as claimed in claim 9, wherein the single preamble is uniquely allocated to the user equipment by the base station.

11 . A method as claimed on any of claims 1 to 10, wherein the control information indicates a plurality of preambles mapped with a plurality of respective beam indexes in a mapping table.

12. A method as claimed in any of claims 1 to 11 , wherein using said preamble in a random access procedure comprises causing the preamble to be transmitted to the base station in a random access subframe.

13. A method as claimed in claim 12, wherein causing the preamble to be transmitted to the base station in a random access subframe comprises causing the preamble to be transmitted to the base station in a random access subframe immediately following the subframe in which the control information is received from the base station.

14. A method as claimed in any of claims 12 or 13, wherein the random access subframe has a subframe index of Ί 5’ or‘40’.

15. A method comprising:

transmitting control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

using said preamble in a random access procedure.

16. A method as claimed in claim 15, comprising: transmitting a plurality of beam reference signals to the user equipment, each beam reference signal being transmitted by the base station on a respective beam.

17. A method as claimed in claim 16, wherein each beam reference signal is transmitted to the user equipment in a sweeping subframe.

18. A method as claimed in claim 17, wherein the sweeping subframe has a subframe index of Ό’ or‘25’.

19. A method as claimed in any of claims 16 to 18, comprising:

receiving beam state information from the user equipment for each beam reference signal.

20. A method as claimed in claim 19, wherein the beam state information comprises receiving beam reference signal received power.

21 . A method as claimed in any of claims 19 or 20, comprising:

receiving beam state information from the user equipment for each beam reference signal with a respective beam index.

22. A method as claimed on any of claims 15 to 21 , wherein the control information indicates a single preamble.

23. A method as claimed in claim 22, wherein the single preamble is uniquely allocated to the user equipment by the base station.

24. A method as claimed on any of claims 15 to 23, wherein the control information comprises a plurality of preambles mapped with a respective beam of the plurality of beams in a mapping table.

25. A method as claimed in any of claims 15 to 24, wherein using said preamble in a random access procedure comprises receiving the preamble from the user equipment in a random access subframe.

26. A method as claimed in claim 25, wherein receiving the preamble from the user equipment in a random access subframe comprises receiving the preamble from the user equipment in a random access subframe immediately following a subframe in which the control information is transmitted by the base station.

27. A method as claimed in any of claims 25 or 26, wherein the random access subframe has a subframe index of Ί 5’ or‘40’.

28. A computer program comprising computer executable instructions which when run on one or more processors perform the following steps:

using said preamble in a random access procedure.

29. A computer program comprising computer executable instructions which when run on one or more processors perform the following steps:

using said preamble in a random access procedure.

30. An apparatus comprising at least one processor, and at least one memory including 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 control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

use said preamble in a random access procedure.

31 . An apparatus comprising at least one processor, and at least one memory including 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:

transmit control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

use said preamble in a random access procedure.

32. An apparatus comprising:

means for receiving control information from a base station, the control information indicating at least one beam of a plurality of beams to be used by a user equipment for communication with the base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

means for using said preamble in a random access procedure.

33. An apparatus comprising:

means for transmitting control information to a user equipment, the control information indicating at least one beam of a plurality of beams to be used by the user equipment for communication with a base station and a preamble to be used by the user equipment for initiating a random access procedure with the base station; and

means for using said preamble in a random access procedure.