CN111165059A

CN111165059A - Handover procedure for wireless networks using beamforming

Info

Publication number: CN111165059A
Application number: CN201780095270.7A
Authority: CN
Inventors: 贺敬; 李海涛; 张力; 姚春海
Original assignee: Nokia Solutions and Networks Oy; Alcatel Lucent SAS
Current assignee: Nokia Solutions and Networks Oy; Alcatel Lucent SAS
Priority date: 2017-09-27
Filing date: 2017-09-27
Publication date: 2020-05-15
Anticipated expiration: 2037-09-27
Also published as: EP3689083A4; WO2019061082A1; CN111165059B; EP3689083A1

Abstract

Various communication systems may benefit from improved methods for handover when beamforming is used. For example, in the case of an intra-network handover or an inter-network handover, it may be advantageous to use a method comprising: the method further includes receiving a dedicated random access channel configuration associated with at least one first downlink beam, determining that the apparatus is not in a coverage area of the at least one first downlink beam, and based on the determination, transmitting a random access message for at least one second downlink beam using the dedicated random access channel configuration associated with the at least one first downlink beam.

Description

Handover procedure for wireless networks using beamforming

Technical Field

The present invention generally relates to an apparatus, method and computer program for handover procedures for wireless networks using beamforming.

Background

Embodiments of the present invention relate to wireless or mobile communication networks such as, but not limited to, global system for mobile communications, GSM, wideband code division multiple access, WCDMA, long term evolution, LTE and/or 5G radio access technologies, which may also be referred to as new radio access technologies NR. Since its establishment, LTE has been widely deployed in various environments involving data communication, and LTE is still being developed by the third generation partnership project 3 GPP. Likewise, 3GPP also developed a standard for 5G/NR. In general, the goal of 3GPP is to further develop and improve wireless cellular systems.

One of the topics related to LTE and 5G/NR in the 3GPP discussion is mobility. When a mobile terminal moves, it may be necessary to handover the mobile terminal from one base station to another to maintain connectivity. Such a handover may be required within the network (intra-network handover) or between networks (inter-network handover). Generally, there is a need to improve the handover procedure to achieve efficient operation.

Beamforming may be used in wireless networks to steer transmission and/or reception to a certain direction for better performance than omni-directional transmission and/or reception. However, if the user equipment moves, a continuous connection should be maintained even if beamforming is used.

Similar enhancements may also be employed in other wireless cellular systems such as GSM and WCDMA, for example. These enhancements may also be utilized in relation to or in combination with a plurality of other wireless systems, such as wireless local area networks, WLANs, and worldwide interoperability for microwave access, WiMAX, systems, in addition to the different wireless cellular systems.

Disclosure of Invention

According to certain embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: the method may include receiving a dedicated random access channel configuration associated with at least one first downlink beam, determining that the apparatus is not in a coverage area of the at least one first downlink beam, and transmitting a random access message for at least one second downlink beam using the dedicated random access channel configuration associated with the at least one first downlink beam based on the determination.

According to some embodiments, the first method may comprise: the method may include receiving a dedicated random access channel configuration associated with at least one first downlink beam, determining that the apparatus is not in a coverage area of the at least one first downlink beam, and transmitting a random access message for at least one second downlink beam using the dedicated random access channel configuration associated with the at least one first downlink beam based on the determination.

According to certain embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: the method further includes transmitting a dedicated random access channel configuration associated with the at least one first downlink beam to the user equipment, and receiving a random access message for the at least one second downlink beam from the user equipment on the dedicated random access channel associated with the at least one first downlink beam.

According to some embodiments, the second method may comprise: the method further includes transmitting a dedicated random access channel configuration associated with the at least one first downlink beam to the user equipment, and receiving a random access message for the at least one second downlink beam from the user equipment on the dedicated random access channel associated with the at least one first downlink beam.

According to some embodiments, a computer program product may be configured to control an apparatus to perform a process according to the first or second method.

According to some embodiments, an apparatus may include means for performing the first or second method.

Drawings

For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

fig. 1 illustrates a conventional procedure for handover;

fig. 2 illustrates an example of a handover procedure according to an embodiment of the present invention;

FIG. 3 illustrates a process according to some embodiments of the inventions;

FIG. 4 illustrates a flow diagram of a method according to an embodiment of the invention;

FIG. 5 illustrates a flow diagram of a method according to an embodiment of the invention;

fig. 6 illustrates an apparatus according to an embodiment of the invention.

Detailed Description

Embodiments of the present invention relate to handover procedures for wireless networks using beamforming and provide improved solutions for handover when beamforming is used.

In the case of wireless communication, radio resources may be allocated in two ways. Dedicated resources may be used by only one device and thus collisions may be avoided. On the other hand, shared resources may be shared among multiple devices, which may lead to a situation in which collisions occur.

For example, a random access channel, RACH, may be utilized to access a wireless communication system, or when a mobile station is handed over from one base station to another within or between networks. Both dedicated resources and shared resources may be used for random access, depending on the situation. Contention-free random access, CFRA, refers to the use of dedicated resources, while contention-based random access, CBRA, refers to the use of shared resources. The RACH resource may be, for example, a preamble, a sequence, a frequency resource, or a time resource. For example, the preamble may include a cyclic prefix CP, a sequence, and a guard time. The sequence may be a Zadoff-Chu sequence or another suitable sequence. Also, the RACH resource may also refer to a set of resources such as two or more preambles, two or more sequences, two or more frequency resources, or two or more time resources. In some embodiments, the RACH resource may be a physical random access channel, a PRACH resource, or a set of PRACH resources.

Dedicated resources and shared resources may also be utilized with beamforming. By using beamforming, transmission and/or reception can be directly steered to optimize communication by adjusting the radiation pattern of the antenna array at the transmitter and/or receiver side. Thus, beamforming may be bidirectional. For example, beamforming can be seen as directing a power lobe in a certain direction. In the case of beamforming, a RACH resource or set of resources may be associated with a downlink beam or set of downlink beams.

If beamforming or any other similar technique is used, the user equipment UE may report per-beam or per-beam set measurement information to the base station. The reported information may be based on the synchronization signal SS and/or the channel state indication reference signal CSI-RS. In some embodiments, this information may be transmitted to the base station BS in a measurement report. For example, the received information may be used at the BS to adjust the resource allocation accordingly.

Fig. 1 illustrates a procedure for an inter-BS handover (i.e., intra-network handover). The invention is described in the context of this architecture, but may be employed in any suitable alternative network architecture, such as for inter-network handover. As a starting point, the UE may be in a CONNECTED state, e.g., in an RRC-CONNECTED state. The source and target base stations may also utilize reporting information about the beam or set of beams in case of an upcoming handover of the UE. The source BS may receive reporting information about a beam or a set of beams from the UE, e.g., in a measurement information message (110).

Also, the source BS may transmit or forward information related to the beam or set of beams to the target BS, e.g., in a handover request message (120). Upon receiving the information, the target BS may perform admission control and select the most appropriate beam for the UE. The target BS may also allocate the dedicated random access channel resources associated with the most appropriate beam to the UE accordingly. If a set of RACH resources is allocated, those resources may be associated with a set of downlink beams.

Thereafter, the target BS may transmit a message, e.g., an acknowledgement message related to the upcoming handover, to the source BS (130). The target BS may also generate an RRCConnect ionReconfiguration message, which may be a part of the message, for the UE. The RRCConnect ionReconfiguration message may also include an information element related to mobilityControlInfo.

The source BS may transmit information included in the received message to the UE, possibly in the form of a handover command (140). That is, the message may be transmitted from the target BS to the UE via the source BS. In some embodiments, the handover command (140) may include at least the cell identity of the target BS. Alternatively or additionally, the handover command (140) may include information required to access the target BS. Such information may be sufficient for the UE to access the target BS. For example, in some cases, the handover command (140) may include information required for CBRA and/or CFRA. In case of beamforming, the handover command (140) may also comprise information about the beam or set of beams.

For example, the target BS may provide the UE with a common RACH configuration as a shared resource and/or a dedicated RACH configuration as a dedicated resource. In some embodiments, the common RACH configuration may be a common RACH resource associated with SS blocks that all UEs may use. In addition, in some embodiments, the dedicated RACH configuration may be a dedicated RACH resource associated with a dedicated SS block and/or associated with a dedicated CSI-RS that only one UE may use.

The common RACH configuration may be identical to the configuration information broadcast in the system information block. Thus, the UE may use the common RACH configuration for performing CBRA. On the other hand, the dedicated RACH configuration may be allocated to only one specific UE for performing CFRA.

If the target BS uses beamforming, the dedicated RACH resource configuration may be associated with one beam or a set of beams. The configuration may be associated with SS block(s) and/or CSI-RS(s). In some embodiments, one RACH resource may be allocated to a UE for performing CFRA, and in some embodiments, a set of RACH resources may be allocated. The dedicated RACH resource configuration may include one RACH resource per beam if a set of RACH resources is allocated. For example, if three dedicated RACH resources are configured to be associated with three beams, the dedicated RACH configuration may include one resource per beam.

After receiving the handover command, the UE may handover to or access the target BS. To this end, the UE may utilize information received in the handover command (140), such as, for example, information required for CBRA and/or CFRA. Once the UE has decided to handover to the target BS, it may send a message, e.g., a handover complete message (150), to the target BS to access the target BS. The transmission of the message may be accomplished by utilizing information required for CBRA and/or CFRA.

However, one problem may be that if beamforming is used at the target BS, the UE may move after it has reported beam measurement information, at least in some cases. In this case, it may happen that the beam or beams indicated in the handover command (140) are no longer suitable for accessing the target BS, i.e. the indicated beam or beams may be invalid. For example, the target BS may allocate a dedicated RACH resource related to the first downlink beam or the first set of downlink beams to the UE. However, if the UE has moved, the quality of the first downlink beam or the first set of downlink beams may be degraded due to the movement of the UE. On the other hand, it may happen that the quality of the second downlink beam or the second set of downlink beams has improved and that the second downlink beam or the second set of downlink beams will be better for the UE at this time.

Thus, if in this case the UE were to transmit a message to the target BS using the configured dedicated RACH resources associated with the first downlink beam(s), the target BS would respond by transmitting the message using the first downlink beam(s). Therefore, the UE will not correctly receive the message from the target BS. Thus, the random access procedure will continue and after several attempts the UE will fall back to CBRA. This will cause a significant delay in the handover procedure. One possible solution might be to configure the UE such that it falls back to CBRA immediately once it notices that the first downlink beam(s) is not suitable for communication. However, CBRA should generally be avoided because CBRA is a shared resource and thus collisions may occur, again increasing latency. That is, the use of dedicated RACH resources (i.e., CFRA) should be preferred over CBRA to provide better success rate and lower latency.

In view of the above disadvantages, certain embodiments of the present invention may improve handover procedures, particularly when beamforming is used at the target BS. Embodiments of the present invention support providing faster random access for mobile UEs. Furthermore, embodiments of the present invention also provide a robust solution in which the UE may not have to fall back to CBRA even if the UE has moved from the coverage area of the first downlink beam(s) to the coverage area of the second downlink beam(s).

For example, if the UE has moved away from the coverage area of the first downlink beam(s) associated with the indicated dedicated RACH resource, the UE may continue to use the dedicated RACH resource, e.g., if the target BS may receive omni-directionally. For this reason, even if the target BS is not moved out of the coverage area of the first downlink beam(s), it may indicate to the UE that it can use the dedicated RACH resource. In this case, the UE may indicate the index of the second downlink beam(s) to the target BS, so that the target BS may transmit a response message to the UE using the second downlink beam(s).

Alternatively, if the UE knows that the target BS can only receive dedicated RACH resources in a certain direction, the UE may quickly fall back to use CBRA for the second downlink beam(s). This may be beneficial, for example, if the uplink is beamformed in the target BS, i.e., the target BS uses beamforming in reception. For this option, even if the target BS moves out of the coverage area of the first downlink beam(s), it may indicate to the UE that it cannot use the dedicated RACH resource. That is, even if the target BS moves out of the coverage area of the first downlink beam(s), it can indicate to the UE whether it can use the dedicated RACH resource.

Even though the allocated dedicated RACH resource may be a resource set, one issue to consider is how many resources should be included in the set. This results in a trade-off between RACH resource consumption and the possibility of the UE using CFRA. Once the dedicated RACH resource is configured to a UE, it will be temporarily unavailable to any other UE. Thus, one network implementation may be to configure a small number of dedicated RACH resources, e.g., only one. However, in that case, the probability of the UE moving outside the coverage of the dedicated RACH resource increases compared to the case where a large amount of RACH resources would be allocated. In practice, RACH resources are limited and therefore, it may not be desirable to reserve many dedicated RACH resources for handover of a single UE. Certain embodiments of the present invention support saving resources of dedicated RACH resources, since fewer resources can be allocated for one UE while also minimizing latency.

Examples of how this can be achieved are provided below. Fig. 2 shows an example of a network scenario according to an embodiment of the present invention. The network may comprise a core network, two or more base stations BS (210, 220) and at least one user equipment UE (230). The BS (210) may be a source BS for handover, and the BS (220) may be a target BS for handover.

In the context of 5G/NR and intra-network handover, the BS (210, 220) may be referred to as a gNB. On the other hand, in the context of LTE and intra-network handover, the BS (210, 220) may be referred to as an eNB. In the case of inter-network handover, BS (210) may be a gNB and BS (220) may be an eNB, or vice versa. However, the present invention is not limited to any particular definition of a BS, i.e., one skilled in the art will understand how to apply the present invention in different wireless systems that may have various names for BSs (210, 220). Likewise, even though the invention is described using the UE (230) as an example, other names may be used, such as mobile station or wireless terminal.

As a starting point, the UE (230) may associate with the BS (210). In some embodiments, the UE may be in an RRC _ CONNECTED state. The UE (230) may perform measurements related to one or more beams and report information related to the measurements to the BS (210). The UE (230) may report, for example, measurements related to the first downlink beam (240) if the received power of the first downlink beam (240) is above a threshold (a4 event) or better than a shift in the received power of a serving beam (A3 event), wherein the serving beam is associated with the BS (210).

Upon detecting a need for a handoff, BS (210) may transmit a message to BS (220) via a fixed backhaul connection. The message may include information related to beam measurements reported by the UE (230). Based on this information, the BS (220) may determine dedicated RACH resources that the UE (230) may use to access the BS (220). Dedicated RACH resources may be used for a beam or a set of beams. Referring to fig. 2, a dedicated RACH resource may be associated with a first downlink beam (240).

The BS (220) may then transmit a message to the BS (210) that includes information about the dedicated RACH. In some embodiments, the message may be in the form of an RRCConnectionReconfiguration message, possibly including a mobilityControlInfo information element. The message may also include an indication or instruction as to whether the UE (230) should continue to use the dedicated RACH resource even though it finds that it has moved away from the coverage area of the first downlink beam (240) associated with the dedicated RACH resource. The BS (210) may transmit or forward the message to the UE (230). That is, the message is transmitted from the BS (220) to the UE (230) via the BS (210).

Referring again to fig. 2, the UE may have moved along the trajectory (260) during the handover procedure. Accordingly, the UE (230) may determine whether the first downlink beam (240) associated with the dedicated RACH is still suitable for communication. In other words, the UE (230) determines whether it has moved away from the coverage area of the first downlink beam (240). The determination may be based on the most recent measurement.

For example, the UE (230) may compare the received power of the first downlink beam (240) to a threshold or offset between the received power of the first downlink beam (240) and the serving beam. For example, if the received power (e.g., reference signal received power, RSRP) is above a threshold, the first downlink beam (240) may be determined to be suitable for communication. However, if the received power is below a threshold, the first downlink beam (240) may be determined to be unsuitable for communication.

In some embodiments, the received power of the first downlink beam (240) may be compared to the received power of the second downlink beam (250). For example, if the received power of the first downlink beam (240) is much lower than the received power of the second downlink beam (250), it may be determined that the first downlink beam (240) is not suitable for communication and the second downlink beam (250) is suitable for communication.

If it is determined that the first downlink beam (240) is not suitable for communication but the second downlink beam (250) is suitable, the UE (230) may indicate this by transmitting a first message to the BS (220) to access the BS (220). The first message may include information related to the second downlink beam (250). Such information may include, for example, measurement information related to the second downlink beam (250), an index related to the second downlink beam (250), or a measurement report related to the second downlink beam (250). The measurement report may also include information relating to one or more other beams. After transmitting the first message to the BS (220), the UE (230) may begin monitoring for or receiving a random access response message from the BS (220) on the second downlink beam (250).

Based on the received information on the second downlink beam (250), the BS (220) may then select the second downlink beam (250) as the appropriate beam instead of the first downlink beam (240) and inform the UE (230) accordingly. The BS (220) may also transmit subsequent downlink messages to the UE (230) by using the selected beam. That is, after receiving the random access response message, the UE (230) may use it to configure for accessing the BS (220) and receive transmissions accordingly.

The new information measured in the first message may relate to one or more downlink beams measured by the UE, or to other assistance information that the target BS may use to identify the current location of the UE (230) and the best beam, and/or to an offset between the allocated beam index and the best beam index. In the scenario of fig. 2, the best beam may be the second downlink beam (250), while the assigned beam index is related to the first downlink beam (240).

The transmission of the first message from the UE (230) to the BS (220) may depend on the indication as to whether the UE (230) should continue to use the dedicated RACH resource even if it is found to have moved away from the coverage area of the first downlink beam (240). For example, the BS (220) may instruct the UE (230) not to use the dedicated RACH resource. In this case, the UE (230) may start the random access procedure immediately using CBRA, i.e. the UE (230) may be instructed to use CBRA if the BS (220) finds that it has moved away from the coverage area of the first downlink beam (240). Thus, the UE may use the CBRA with the common RACH resources associated with the beam it is measured to be appropriate (e.g., the second downlink beam (250) in fig. 2). In this case, if the dedicated RACH resource associated with the first downlink beam (240) is to be used, the BS (220) is anyway unable to correctly receive the first message, since the BS will receive with beamforming.

Also, the BS (220) may instruct the UE (230) to continue using the dedicated RACH resource even though it finds that it has moved away from the coverage area of the first downlink beam (240). In this case, the UE (230) may transmit a random access message for a suitable beam (e.g., the second downlink beam (250) in fig. 2) using the dedicated RACH resources. The UE may indicate in the first message, for example, an index of the suitable beam or some other information related to the suitable beam. In some embodiments, if the UE (220) is using transmit beamforming, it may form a beam according to the downlink beam it is measured to be appropriate.

FIG. 3 illustrates a process according to some embodiments of the inventions. During or before the handover procedure, the UE may receive a dedicated RACH configuration associated with the first downlink beam(s) in step 310. In addition, if the UE finds in step 320 that it has moved away from the coverage area of the first downlink beam(s), the UE may receive instructions related to using the dedicated RACH configuration. In some embodiments, the instructions may be received using dedicated signaling. However, although such instructions may be optional. In some embodiments, the UE may be configured to use a dedicated RACH configuration if the UE finds that by default it has moved away from the coverage area of the first downlink beam(s), e.g., based on the UE's own capabilities. In this case, the UE may receive the information in a broadcast message such as, for example, in a system information block SIB.

Thereafter, in step 330, the UE may determine whether it is in the coverage area of the first downlink beam(s). If so, the UE may transmit a random access, RA, message for the first downlink beam(s) in step 340 using the dedicated RACH configuration associated with the first downlink beam. Thereafter, the UE may begin monitoring for, receiving random access response messages on the first downlink beam(s).

However, if the UE determines that it is not in the coverage area of the first downlink beam(s), then the process may proceed to step 350, where, for example, if the UE finds that it has moved away from the coverage area of the first downlink beam(s), based on the received instructions relating to the use of the dedicated RACH configuration, the UE may determine whether the dedicated RACH configuration may be used for the second downlink beam(s). If so, in step 360, the UE may transmit a random access message for the second downlink beam(s) using the dedicated RACH configuration. On the other hand, if it is determined that the dedicated RACH configuration may not be used for the second downlink beam(s), the UE may directly transmit a RA message for the second downlink beam using CBRA in step 360. Thereafter, the UE may start monitoring, receiving random access response messages on the second downlink beam(s). Once the UE has received the random access response message, it may use the information therein to receive subsequent downlink transmissions.

Then, FIG. 4 illustrates a method according to some embodiments. In some embodiments, the UE may perform the method. As shown in fig. 4, the method may include receiving a dedicated random access channel configuration associated with at least one first downlink beam in 410. In some embodiments, the UE may receive a dedicated random access channel configuration from the BS. In case of handover, the BS may be a source BS for handover. The at least one first downlink beam and/or the at least one second downlink beam may comprise one downlink beam or a set of downlink beams of the target BS, but not all.

The method may further include determining, at 420, that the UE is not in a coverage area of the at least one first downlink beam. Moreover, the method may include determining that the UE is not in the coverage area of the at least one first downlink beam, e.g., by examining measurements related to the at least one first downlink beam. Alternatively or additionally, the method may comprise determining that the UE is not in the coverage area of the at least one first downlink beam by comparing the received power of the at least one first downlink beam to a threshold. Likewise, the method may further include determining that the UE is in the coverage area of the at least one second downlink beam, which may be accomplished by using the same procedure as determining that the UE is not in the coverage area of the at least one first downlink beam.

In some embodiments, the method may further comprise: if or when it is determined that the apparatus is not in the coverage area of the at least one first downlink beam, i.e. the at least one first downlink beam is not suitable for communication, an instruction to use a dedicated random access channel configuration for transmitting random access messages for the at least one second downlink beam is received.

Additionally or alternatively, the method may further comprise: receiving an instruction not to use the dedicated random access channel configuration associated with the at least one second downlink beam if or when it is determined that the UE is not in the coverage area of the at least one first downlink beam. In other words, the method may further include: receiving an instruction to use contention-based random access related to the at least one second downlink beam if or if it is determined that the UE is not in the coverage area of the at least one first downlink beam.

The method may further comprise: at step 430, a random access message for at least one second downlink beam is transmitted based on the determination to use a dedicated random access channel configuration associated with the at least one first downlink beam. In case of handover, the method may include: a dedicated random access channel configuration for the at least one first downlink beam is received from the source base station and a random access message is transmitted to the target base station for handover.

The method may further comprise: transmitting a random access message using a dedicated random access channel based on the received instruction. In some embodiments, the method may further comprise: after the transmission of the random access message, monitoring or receiving a random access response message from the base station on the at least one second downlink beam is started. Moreover, the method can include receiving a subsequent downlink transmission based on the information included in the random access response message.

Alternatively or additionally, the method may comprise transmitting the random access message using contention-based random access. The decision to transmit the random access message using contention based random access may be based on a received instruction not to use a dedicated random access channel configuration for transmitting the random access message for the at least one second downlink beam.

The random access message may include a preamble associated with the dedicated random access channel configuration and information related to the at least one second downlink beam. The information may comprise, for example, an index associated with the at least one second downlink beam, any other information that may be used for calculating the index associated with the at least one second beam, measurement information related to the at least one second downlink, or a new measurement report.

FIG. 5 illustrates another method according to some embodiments. In some embodiments, the method may be performed by a base station. For example, in case of handover, the method may be performed by the target base station. The method can comprise the following steps: in 510, a dedicated random access channel configuration associated with the at least one first downlink beam is transmitted to the user equipment. Alternatively or additionally, the method may comprise: transmitting an instruction not to use a dedicated random access channel configuration for transmitting a random access message for the at least one second downlink beam. Such instructions may be given, for example, for a scenario in which the user equipment may determine that the UE is not in the coverage area of the at least one first downlink beam.

In step 520, the method may include: for example, if an instruction to use the dedicated random access channel configuration has been transmitted to transmit a random access message for the at least one second downlink beam and the user equipment determines that it is not in the coverage area of the at least one first downlink beam, a random access message for the at least one second downlink beam is received from the user equipment on the dedicated random access channel associated with the at least one first downlink beam. As such, the method may further comprise: for example, if an instruction to not use the dedicated random access channel configuration has been transmitted to transmit a random access message for the at least one second downlink beam and the user equipment has determined that it is not in the coverage area of the at least one first downlink beam, the random access message is received using contention-based random access.

Fig. 6 illustrates an apparatus (10) according to an embodiment of the invention. The apparatus (10) may be a wireless device such as a user equipment, for example. In other embodiments, such (10) may be a base station, an access point, a software defined network, an SDN controller, a cloud base station controller, or a centralized base station controller, for example.

The wireless device or user equipment may be a mobile station, a MS provided with wireless communication capabilities, such as a mobile phone or smart phone or multimedia device, a computer provided with wireless communication capabilities, such as a tablet computer, a personal data or digital assistant PDA provided with wireless communication capabilities, a portable media player, a digital camera, a camcorder, a navigation unit provided with wireless communication capabilities, or any combination thereof. The wireless device or user device may be a sensor or smart meter or other device that may be generally configured for a single location. Additionally, the wireless device or user equipment may be a device-to-device user equipment or a device for machine type communication.

The apparatus (10) may include a processor (22) to process information and execute instructions or operations. The processor (22) may be any type of general or special purpose processor. Although a single processor (22) is shown in fig. 6, multiple processors may be used according to other embodiments. As examples, the processor (22) may also include one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor DSP, a field programmable gate array FPGA, an application specific integrated circuit (SIC, and a processor based on a multi-core processor architecture.

The apparatus (10) may further include a memory (14) coupled to the processor (22) to store information and instructions that may be executed by the processor (22). The memory (14) may be one or more memories and may be of any type suitable to the local application environment and may be implemented using any suitable volatile or non-volatile data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. For example, the memory (14) may include any combination of random access memory RAM, read only memory ROM, static storage devices such as magnetic or optical disks, or any other type of non-transitory machine or computer readable medium. The instructions stored in the memory (14) may include program instructions or computer program code that, when executed by the processor (22), enable the apparatus (10) to perform the tasks described herein.

The apparatus (10) may also include one or more antennas (not shown) to transmit signals and/or data to and/or receive signals and/or data from the apparatus (10). The apparatus (10) may further include a transceiver (28), the transceiver (28) modulating information onto a carrier waveform for transmission by the antenna(s), and demodulating information received via the antenna(s) for further processing by other elements of the apparatus (10). In other embodiments, the transceiver (28) may be capable of directly transmitting and receiving signals or data.

The processor (22) may perform functions associated with operation of the apparatus (10) including, but not limited to, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus (10), including procedures related to communication resource management.

In certain embodiments, the memory (14) stores software modules that provide functionality when executed by the processor (22). The modules may include an operating system (15) that provides operating system functionality for the device (10). The memory may also store one or more functional modules (18), such as applications or programs, to provide additional functionality for the apparatus (10). The components of the apparatus (10) may be implemented in hardware or as any suitable combination of hardware and software.

The described features, advantages, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

Moreover, one of ordinary skill in the art will readily appreciate that the invention discussed above may be practiced with steps in a different order and/or with hardware elements in configurations different from those disclosed. Thus, while the invention has been described based upon these preferred embodiments, it would be apparent to those of ordinary skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.

In an example embodiment, an apparatus, such as a user equipment or a base station, may comprise means for performing the above embodiments and any combination thereof.

In another example embodiment, an apparatus, such as a user equipment or a base station, may include 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 to perform at least the above embodiments and any combination thereof.

In another exemplary embodiment, the computer program product may be configured to control an apparatus to perform a process according to the above embodiments and any combination thereof. The computer program product may be embodied on a non-transitory computer readable medium.

Claims

1. 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:

receiving a dedicated random access channel configuration associated with at least one first downlink beam;

determining that the apparatus is not in a coverage area of the at least one first downlink beam; and

transmitting a random access message for at least one second downlink beam using the dedicated random access channel configuration associated with the at least one first downlink beam based on the determination.

2. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus at least to:

determining that the apparatus is in a coverage area of the at least one second downlink beam.

3. The apparatus of claim 1 or claim 2, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

receiving instructions to transmit the random access message for the at least one second downlink beam using the dedicated random access channel configuration when it is determined that the apparatus is not in the coverage area of the at least one first downlink beam.

4. The apparatus of claim 3, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus at least,

transmitting the random access message using the dedicated random access channel based on the received instruction.

5. The apparatus according to any of the preceding claims, wherein the random access message comprises: a preamble associated with the dedicated random access channel configuration and information related to the at least one second downlink beam.

6. The apparatus of any preceding claim, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

starting monitoring or receiving a random access response message from a base station on the at least one second downlink beam after the transmission of the random access message.

7. The apparatus of any preceding claim, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

receiving an instruction to use contention-based random access when it is determined that the apparatus is not in the coverage area of the at least one first downlink beam.

8. The apparatus of any preceding claim, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

transmitting the random access message using contention-based random access.

9. The apparatus of any preceding claim, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

receiving the dedicated random access channel configuration for the at least one first downlink beam from a source base station; and

and transmitting the random access message to a target base station for switching.

10. The apparatus according to any of the preceding claims, wherein the random access message comprises measurement information related to the at least one second downlink beam.

11. The apparatus of any preceding claim, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

determining that the apparatus is not in the coverage area of the at least one first downlink beam by comparing a received power of the at least one first downlink beam to a threshold.

12. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code,

transmitting to the user equipment a dedicated random access channel configuration associated with the at least one first downlink beam; and

receiving a random access message for at least one second downlink beam from the user equipment on the dedicated random access channel associated with the at least one first downlink beam.

13. The apparatus of claim 12, wherein the at least one memory and the computer program code are configured to, with the at least one processor, further cause the apparatus at least to:

transmitting an instruction to use the dedicated random access channel configuration for transmitting the random access message for the at least one second downlink beam when it is determined that the user equipment is not in the coverage area of the at least one first downlink beam.

14. The apparatus according to claim 12 or 13, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

transmitting an instruction not to use the dedicated random access channel configuration for transmitting the random access message for the at least one second downlink beam when it is determined that the user equipment is not in the coverage area of the at least one first downlink beam.

15. The apparatus of any of claims 12 to 14, wherein the at least one memory and the computer program code configured to, with the at least one processor, further cause the apparatus at least to:

receiving the random access message using contention-based random access.

16. The apparatus according to any of claims 12 to 15, wherein the apparatus is a target base station for handover.

17. A method, comprising:

18. The method of claim 17, further comprising,

19. The method of claim 17 or claim 18, further comprising,

20. The method of claim 19, further comprising,

21. The method according to any of claims 17 to 20, wherein the random access message comprises: a preamble associated with the dedicated random access channel configuration and information related to the at least one second downlink beam.

22. The method of any of claims 17-21, further comprising,

23. The method of any of claims 17 to 22, further comprising,

24. The method of any of claims 17 to 23, further comprising,

transmitting the random access message using contention-based random access.

25. The method of any of claims 17 to 24, further comprising,

26. The method according to any of claims 17 to 25, wherein the random access message comprises measurement information related to the at least one second downlink beam.

27. The method of any of claims 17 to 26, further comprising,

28. A method, comprising:

29. The method of claim 28, further comprising,

30. The method of claim 28 or claim 29, further comprising,

31. The method of any of claims 28 to 30, further comprising,

receiving the random access message using contention-based random access.

32. The method of any of claims 28 to 31, wherein the apparatus is a target base station for handover.

33. An apparatus comprising means for performing the method of claims 17-27 or claims 28-32.

34. A computer program product configured to control an apparatus to perform a process according to the method of claims 17 to 27 or claims 28 to 32.