TECHNICAL FIELD

The present application relates to the field of wireless communications, and more particularly to a client device, and related methods and computer programs . BACKGROUND

In some wireless systems, such as so called New Radio (NR) systems, beam sweeping procedures are utilized. There are sweeping subframes, each of which may comprise several blocks. Each block may comprise one or multiple symbols, and each block may be transmitted and/or received with a spatial beam(s) . There may be sweeping subframes with configurable resource allocation in terms of periodicity and radio resources.

Sweeping subframes are used for downlink (DL) common control signaling needed by a client device (e.g. a user equipment) to perform initial cell search, DL synchronization, system information signaling, and/or cell/beam measurements.

For uplink (UL) random access, beam sweeping allows utilizing beamforming gain and it allows a network node (e.g. a general NodeB (gNB) of New Radio) to determine a second message (Msg 2) DL transmit (Tx) beam. The second message may comprise a random access response (RAR) . Random access (RACH) resources and/or preamble indices are associated with DL beamformed signals/channels which can be configured by the network node. Herein, a RACH resource comprises one or more time-frequency resource for sending the RACH preamble. A preamble index comprises a preamble sequence index. The preamble index may also comprise an orthogonal cover code (OCC) index when OCC is supported.

The client device attempts to select a best or preferred DL beam based on DL measurements of DL signals/channels on different DL beams. As illustrated by diagram 100 in Figure 1, based on a corresponding association between the DL signal/channel and the RACH resources and/or the preamble indices, the client device selects the corresponding RACH resources and/or the preamble indices for RACH preamble transmission. If the network node detects a first message (Msgl) transmission, the network node can learn which DL beam the client device prefers according to the association and the network node may send a Msg2 corresponding to the transmitted RACH preamble. If the client device does not receive a RAR, the client device may retransmit Msgl on another RACH occasion.

The NR RACH Msgl retransmission may utilize beam switching and/or power ramping for multi-beam operation. However, current schemes for beam switching and power ramping may result in e.g. unnecessarily high transmission power and/or access delay for at least some of the retransmissions.

SUMMARY

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

It is an object of the invention to provide improved multi-beam based wireless communication. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect a client device is provided, the client device comprising: a transceiver configured to transmit a first message comprising a random access preamble to a network node device via a first uplink beam pair and to retransmit the first message as needed, via at least a second uplink beam pair, wherein each uplink beam pair comprises a transmit beam of the client device and a receive beam of the network node device, and each uplink beam pair has at least one of its transmit beam or receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs; and a processor configured to set a separate power ramping counter for the transmissions of the first message per each uplink beam pair. Power ramping for first message retransmissions may be based on each uplink beam pair, thereby allowing the client device to use previous transmit power information of the same uplink beam pair. The client device may select more than one preferred random access resources and/or preamble indices based on downlink measurements during random access procedures, thereby allowing decreased access latency and/or decreased uplink interference on a specific receive beam of the network node.

In a further implementation form of the first aspect, the processor is further configured to set at least one power setting parameter for the transmission of the first message per each of the at least one uplink beam pair, wherein the at least one power setting parameter comprises at least one of an initial transmit power or an initial received target power configured by the network node device.

In a further implementation form of the first aspect, the processor is further configured to set the initial transmit power as a function of downlink path loss .

In a further implementation form of the first aspect, the processor is further configured to set an initial value for each power ramping counter.

In a further implementation form of the first aspect, the processor is further configured to change the power ramping counter for a given uplink beam pair independent of power ramping counters for any other uplink beam pairs.

In a further implementation form of the first aspect, in response to the transceiver receiving a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device within a given time period: the processor is further configured to cause the transceiver to stop subsequent retransmissions of the first message at least for contention-free random access .

In a further implementation form of the first aspect, in response to the transceiver failing to receive a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device within a given time period, the random access preamble having been transmitted via a given uplink beam pair out of multiple uplink beam pairs: the processor is further configured to cause the transceiver to retransmit the first message via another uplink beam pair before performing power ramping .

In a further implementation form of the first aspect, the processor is further configured to cause the transceiver to retransmit the first message via the given uplink beam for a predetermined amount of times before the retransmission via the another uplink beam pair .

In a further implementation form of the first aspect, in response to the transceiver failing to receive a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device within a given time period, the random access preamble having been transmitted via a given uplink beam pair out of multiple uplink beam pairs: the processor is further configured to cause the transceiver to retransmit the first message with power ramping via the given uplink beam pair for a predetermined amount of times before retransmission via another uplink beam pair out of the multiple uplink beam pairs. Furthermore, two random access preambles can be sent in one random access beam sweeping subframe since for two successive retransmissions the receive beam is changed. Hence, there is no need to wait for a new random access beam sweeping subframe to appear to send the 1st, 3rd, 5th, and 7th retransmissions since these retransmissions can be sent in the same random access beam sweeping subframe as the respective initial transmission, and the 2nd, 4th, and 6th retransmissions, thereby allowing at least doubling the frequency of random access preamble transmissions.

In a further implementation form of the first aspect, the predetermined amount of times is configured by the network node device.

In a further implementation form of the first aspect, the processor is further configured to set a maximum total number of transmissions on all beam pairs, wherein the maximum total number is configured by the network node device or a predefined value.

In a further implementation form of the first aspect, the processor is further configured to set a maximum total number of transmissions on each beam pair, wherein the maximum total number is configured by the network node device or a predefined value.

In a further implementation form of the first aspect, the processor is further configured to perform at least one retransmission in a single random access beam sweeping procedure of the network device by changing receive beams of the uplink beam pairs for two consecutive preamble transmissions.

In a further implementation form of the first aspect, different receive beams of the uplink beam pairs are associated with different uplink resources used for transmitting the first message.

According to a second aspect a method is provided, the method comprising: transmitting a first message comprising a random access preamble from a client device to a network node device via a first uplink beam pair, wherein each uplink beam pair comprises a transmit beam of the client device and a receive beam of the network node device, and each uplink beam pair has at least one of its transmit beam or receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs; and retransmitting the first message as needed via at least a second uplink beam pair, wherein a separate power ramping counter is set for the transmissions of the first message per each uplink beam pair.

According to a third aspect a computer program is provided, the computer program comprising program code configured to perform the method of the second aspect, when the computer program is executed on a computer.

DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:

Fig. 1 is a diagram illustrating beam sweeping;

Fig. 2A is a block diagram illustrating a client device according to an embodiment;

Fig. 2B is a block diagram illustrating a network node device according to an embodiment; and

Fig. 3A is a signaling diagram illustrating a method according to an example;

Fig. 3B is a signaling diagram illustrating a method according to an example;

Fig. 3C is a signaling diagram illustrating a method according to an example; and

Figs. 4A-4D are diagrams further illustrating beam pair switching according to examples.

Like references are used to designate like parts in the accompanying drawings. DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings is intended as a description of the embodiments and is not intended to represent the only forms in which the embodiment may be constructed or utilized. However, the same or equivalent functions and structures may be accomplished by different embodiments.

A client device 200 and a network node device 210 will be described in detail using Fig. 2A and Fig. 2B. Some of the features of the described devices are optional features which provide further advantages. Furthermore, functionalities of the client device 200 and the network node device 210 according to embodiments of the present invention will be described later in more detail in the following descriptions of Fig. 3A to Fig. 3C using four different example scenarios.

Fig. 2A is a block diagram illustrating a client device 200 according to an embodiment. The client device may be any of various types of devices used directly by an end user entity and capable of communication in a wireless network, such as user equipment (UE) . Such devices include but are not limited to smartphones, tablet computers, smart watches, lap top computers, Internet-of-Things (IoT) devices etc. Although embodiments may be described in terms of a client device, it is by way of example and in no way a limitation .

The client device 200 comprises a transceiver 201 that is configured to transmit a first message comprising a random access preamble to the network node device 210 via a first uplink beam pair and to retransmit the first message as needed, via at least a second uplink beam pair. The first message may comprise a Message 1 (Msgl) of a random access procedure of a fifth- generation wireless communication system or a New Radio wireless communication system. The random access preamble may comprise a RACH (Random Access Channel) preamble of the random access procedure of the fifth- generation wireless communication system or the New Radio wireless communication system.

Each uplink beam pair comprises a transmit beam of the client device 200 and a receive beam of the network node device 210. Furthermore, each uplink beam pair has at least one of its transmit beam or receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs. That is, each uplink beam pair may have its transmit beam different from the respective transmit beams in all the other uplink beam pairs, or each uplink beam pair may have its receive beam different from the respective receive beams in all the other uplink beam pairs, or each uplink beam pair may have both its transmit beam and receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs .

The client device 200 further comprises a processor 202 that is configured to set a separate power ramping counter for the transmissions of the first message per each uplink beam pair. Or in other words, each uplink beam pair has its own associated power ramping counter. The processor 202 may include e.g. one or more of various processing devices, such as a coprocessor, a microprocessor, a controller, a digital signal processor (DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, or the like.

The client device 200 may further comprise a memory 203 that is configured to store e.g. computer programs and the like. The memory 203 may include one or more volatile memory devices, one or more non ^¬ volatile memory devices, and/or a combination of one or more volatile memory devices and non-volatile memory devices. For example, the memory 203 may be embodied as magnetic storage devices (such as hard disk drives, floppy disks, magnetic tapes, etc.), optical magnetic storage devices, and semiconductor memories (such as mask ROM, PROM (programmable ROM) , EPROM (erasable PROM), flash ROM, RAM (random access memory), etc.).

According to an embodiment, the processor 202 is further configured to set at least one power setting parameter for the transmission of the first message per each of the at least one uplink beam pair, wherein the at least one power setting parameter comprises at least one of an initial transmit power or an initial received target power configured by the network node device 210.

According to an embodiment, the processor 202 is further configured to set the initial transmit power as a function of downlink path loss.

For example, the initial power setting may be an initial transmit power PpRACH_initiai as the following equations with counter value TRANSMISSION_COUNTER equal to 0, or it may be an initial received target power PREAMBLE_INITIAL_RECEIVED_ TARGET_POWER :

PpRACH_initial =Rlin { PcMAX (ί ) ,

PREAMBLE_INITIAL_RECEIVED_ TARGET_POWER+PL } , where PCMAX(I) is the configured maximum transmit power in subframe I, PL is the measured path loss for the specific beam pair, and PREAMBLE_INITIAL_RECEIVED_ TARGET_POWER is set as:

PREAMBLE_INITIAL_RECEIVED_ TARGET_POWER=

PREAMBLE_INITIAL_RECEIVED_ TARGET + TRANSMISSION_COUNTER * POWER_RAMPING_STEP, and POWER_RAMPING_STEP is a value configured e.g. by the network node device 210 or it may be a predefined value. According to an embodiment, the processor 202 is further configured to set an initial value (e.g. 0) for each power ramping counter.

According to an embodiment, the processor 202 is further configured to change the power ramping counter for a given uplink beam pair independent of power ramping counters for any other uplink beam pairs.

According to an embodiment, in response to the transceiver 201 receiving a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period, the processor 202 is further configured to cause the transceiver 201 to stop subsequent retransmissions of the first message at least for contention-free random access. The second message may comprise a Message 2 (Msg2) of the random access procedure of the fifth-generation wireless communication system or the New Radio wireless communication system. The random access response may comprise a Random Access Response (RAR) of the random access procedure of the fifth-generation wireless communication system or the New Radio wireless communication system.

According to an embodiment, in response to the transceiver 201 failing to receive a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period, the random access preamble having been transmitted via a given uplink beam pair out of multiple uplink beam pairs, the processor 202 is further configured to cause the transceiver 201 to retransmit the first message via another uplink beam pair before performing power ramping.

According to an embodiment, the processor 202 is further configured to cause the transceiver 201 to retransmit the first message via the given uplink beam for a predetermined amount of times before the retransmission via the another uplink beam pair. According to an embodiment, in response to the transceiver 201 failing to receive a second message comprising a random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period, the random access preamble having been transmitted via a given uplink beam pair out of multiple uplink beam pairs: the processor 202 is further configured to cause the transceiver 201 to retransmit the first message with power ramping via the given uplink beam pair for a predetermined amount of times before retransmission via another uplink beam pair out of the multiple uplink beam pairs.

According to an embodiment, the predetermined amount of times is configured by the network node device 210.

According to an embodiment, the processor 202 is further configured to set a maximum total number of transmissions on all beam pairs, wherein the maximum total number is configured by the network node device 210 or a predefined value.

According to an embodiment, the processor 202 is further configured to set a maximum total number of transmissions on each beam pair, wherein the maximum total number is configured by the network node device 210 or a predefined value.

According to an embodiment, the processor 202 is further configured to perform at least one retransmission in a single random access beam sweeping procedure of the network device 210 by changing receive beams of the uplink beam pairs for two consecutive preamble transmissions.

According to an embodiment, different receive beams of the uplink beam pairs are associated with different uplink resources used for transmitting the first message.

Fig. 2B is a block diagram illustrating a network node device 210 according to an embodiment. The network node device 210 may be e.g. a base station, such as a macro-eNodeB, a pico-eNodeB, a home eNodeB, a fifth-generation base station (gNB) or any such device providing an air interface for client devices to connect to the wireless network via multi-beam based wireless transmissions. The network node device 210 comprises a processor 212 and a transceiver 211 which may be used to implement the functionalities described later in more detail in the following descriptions of Fig. 3A to Fig. 3C and Fig. 4A to Fig. 4D.

Fig. 3A is a signaling diagram illustrating a method according to an example. The example of Fig. 3A may be used e.g. when the transceiver 201 receives the second message comprising the random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period.

At operation 301, the network node device 210 configures corresponding associations between downlink signals/channels and random access or random access channel (RACH) resources and/or preamble indices. As a result, each downlink signal/channel is associated with a corresponding set of uplink RACH resources, as illustrated in Fig. 1. Herein, a RACH resource comprises one or more time-frequency resource (s) for sending the RACH preamble. A preamble index comprises a preamble sequence index. The preamble index may also comprise an orthogonal cover code (OCC) index when OCC is supported.

At operation 302, the network node device 210 transmits beamformed downlink signals/channels.

At operation 303, the client device 200 selects one or multiple downlink signals/channels based e.g. on downlink measurements of downlink signals/channels on various downlink beams.

At operation 304, based on the configured associations between the downlink signals/channels and the random access resources and/or the preamble indices, the client device 200 selects the corresponding random access resources and/or the preamble indices for the random access preamble transmission. Accordingly, if the network node 210 detects a first message transmission at operation 309, the network node 210 will be able to learn which downlink beam the client device 200 prefers based on the associations of operation 301, and the network node 210 may send a second message at operation 310 corresponding to the transmitted random access preamble. Each random access resource and preamble index corresponds to one or multiple receive beams of the network node device 210. In other words, at operation 304 the client device 200 effectively selects which receive beam(s) of the network node device 210 will be used, due to the associations configured between the downlink signals/channels and the uplink RACH resources at operation 301. By selecting the time-frequency resource (s) the client device 200 selects the uplink receive beam(s) of the network node device 210 for use.

At operation 305, the client device 200 selects one or multiple transmit beams for each random access resource and/or preamble index, which generates one or multiple uplink transmit-receive beam pairs between the client device 200 and the network node device 210. Each uplink beam pair has at least one of its transmit beam or receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs .

At operation 306, the client device 200 sets at least one power setting parameter for the first message per each uplink transmit-receive beam pair. The at least one power setting parameter may comprise at least one of an initial transmit power or an initial received target power configured by the network node device 210. The initial transmit power may be a function of the path loss obtained with downlink measurements.

At operation 307, the client device 200 sets a power ramping counter per each uplink transmit-receive beam pair. The initial value of each power ramping counter may be e.g. 0. Furthermore, the client device 200 may change the power ramping counter for a given uplink beam pair independent of power ramping counters for any other uplink beam pairs. At operation 308a, the client device 200 transmits the first message comprising the random access preamble to the network node device 210, via a first uplink beam pair. As described above, each uplink beam pair comprises a transmit beam of the client device 200 and a receive beam of the network node device 210, and each uplink beam pair has at least one of its transmit beam or receive beam different from the respective transmit beams and receive beams in all the other uplink beam pairs, and a separate power ramping counter is set for the transmissions of the first message per each uplink beam pair. Furthermore, different receive beams of the uplink beam pairs may be associated with different uplink resources used for transmitting the first message, as discussed above in connection with operations 301 to 304.

Based on the received first message comprising the random access preamble and the associations configured in operation 301, the network node device 210 determines the downlink beam preferred (and selected in operation 305) by the client device 200, operation 309.

At operation 310, the network node device 210 transmits a second message comprising a random access response corresponding to the received random access preamble.

In the example of Fig. 3A, the client device 200 receives the second message comprising the random access response within a given time period at operation 310. Accordingly, subsequent retransmissions of the first message are stopped at least for contention-free random access, and the client device 200 proceeds to transmit uplink signals/channels.

Fig. 3B is a signaling diagram illustrating a method according to another example. The example of Fig. 3B may be used e.g. when the transceiver 201 fails to receive the second message comprising the random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period, and the random access preamble was transmitted via a given uplink beam pair out of multiple uplink beam pairs.

In the example of FIG. 3B, operations 301-307 are substantially similar to their counterparts in the example of FIG. 3A, so their descriptions are not repeated here in detail.

At operation 308b, the client device 200 transmits the first message comprising the random access preamble to the network node device 210, via a given uplink beam pair out of multiple uplink beam pairs (e.g. via a first uplink beam pair) .

Based on the received first message comprising the random access preamble and the associations configured in operation 301, the network node device 210 determines the downlink beam preferred (and selected in operation 305) by the client device 200, operation 309. However, in the example of Fig. 3B, the network node device 210 may fail to receive the first message, in which case operation 309 may fail to happen.

If operation 309 is performed, then at operation 310 the network node device 210 transmits the second message comprising the random access response corresponding to the received random access preamble.

In the example of Fig. 3B, the client device 200 fails to receive the second message comprising the random access response within the given time period at operation 310. Accordingly, the client device 200 retransmits the first message via another uplink beam pair (e.g. via a second uplink beam pair), operation 311b.

If the client device 200 again fails to receive the second message comprising the random access response within the given time period, the client device 200 performs power ramping on one of the uplink beam pairs previously used in the retransmissions (e.g. on the first or second uplink beam pair), operation 312b.

In the example of Fig. 3B, the client device 200 performs beam pair switching before ramping transmission power for the retransmissions of the first message. Fig. 4A and Fig. 4B further illustrate this. In the drawings shown in Fig. 4A-4D an active beam is filled with solid black. An inactive beam is is not filled.

The diagram 410 of Fig. 4A illustrates the client device 200 selecting two RACH resources corresponding to two Rx beams at the network node and having three uplink transmit-receive (UL Tx-Rx) beam pairs 411, 412, 413 for Msgl (re) transmission . Accordingly, there are three power ramping counters 414, one for each of the three UL Tx-Rx beam pairs 411, 412, 413. Fig. 4A illustrates the transmission sequence of different Msgl (re) transmissions, and time gaps between two Msgl transmissions are not limited to be the same. The counter on each UL Tx-Rx beam pair increases independently. In this example, the client device 200 attempts to retransmit Msgl on another beam pair before ramping (i.e. increasing) the transmission power on the same beam pair (except for the 7 ^th retransmission) .

In the example of Fig. 4A, the initial transmission is performed with the UL Tx-Rx beam pair 411 with its power ramping counter value 414 being 0. The first retransmission is performed with the UL Tx-Rx beam pair 412 with its power ramping counter value 414 being 0. The second retransmission is performed with the UL Tx-Rx beam pair 413 with its power ramping counter value 414 being 0. At this point, the client device 200 has attempted to retransmit Msgl on each beam pair it has been chosen before. Accordingly, the third retransmission is performed with the UL Tx-Rx beam pair 413 with its power ramping counter value 414 increased to 1. The fourth retransmission is performed with the UL Tx-Rx beam pair 411 with its power ramping counter value 414 increased to 1. The fifth retransmission is performed with the UL Tx-Rx beam pair 412 with its power ramping counter value 414 increased to 1. At this point, the client device 200 has again attempted to retransmit Msgl on each beam pair. Accordingly, the sixth retransmission is performed with the UL Tx-Rx beam pair 413 with its power ramping counter value 414 increased to 2. Then, the seventh retransmission is performed with the UL Tx-Rx beam pair 413 with its power ramping counter value 414 increased to 3.

The diagram 420 of Fig. 4B illustrates the client device 200 again selecting two RACH resources and again having three UL Tx-Rx beam pairs 421, 422, 423. In this example, the UL Rx pattern at the network node device 210 is different from that in Fig. 4A, and for the second retransmission the client device 200 may use either the left side Tx beam or the right side Tx beam since both beam pairs are candidate beam pairs for Msgl transmission. But since in this example the beam pair is switched before increasing its power ramping counter value 424, the client device 200 uses the right side Tx beam to enable another beam pair to retransmit Msgl in order to avoid ramping power up which would happen if the left side beam were used.

In the example of Fig. 4B, the initial transmission is performed with the UL Tx-Rx beam pair

421 with its power ramping counter value 424 being 0. The first retransmission is performed with the UL Tx-Rx beam pair 422 with its power ramping counter value 424 being 0. The second retransmission is performed with the UL Tx-Rx beam pair 423 with its power ramping counter value 424 being 0. At this point, the client device 200 has attempted to retransmit Msgl on each beam pair. Accordingly, the third retransmission is performed with the UL Tx-Rx beam pair 422 with its power ramping counter value 424 increased to 1. The fourth retransmission is performed with the UL Tx-Rx beam pair 421 with its power ramping counter value 424 increased to 1. The fifth retransmission is performed with the UL Tx-Rx beam pair

422 with its power ramping counter value 424 increased to 2. The sixth retransmission is performed with the UL

Tx-Rx beam pair 423 with its power ramping counter value 424 increased to 1. Then, the seventh retransmission is performed with the UL Tx-Rx beam pair 422 with its power ramping counter value 424 increased to 3. Fig. 3C is a signaling diagram illustrating a method according to yet another example. The example of Fig. 3C may be used e.g. when the transceiver 201 fails to receive the second message comprising the random access response corresponding to the transmitted random access preamble from the network node device 210 within a given time period, and the random access preamble was transmitted via a given uplink beam pair out of multiple uplink beam pairs.

In the example of FIG. 3C, operations 301-307 are substantially similar to their counterparts in the example of FIG. 3A, so their descriptions are not repeated here in detail.

At operation 308b, the client device 200 transmits the first message comprising the random access preamble to the network node device 210, via a given uplink beam pair out of multiple uplink beam pairs.

Based on the received first message comprising the random access preamble and the associations configured in operation 301, the network node device 210 determines the downlink beam preferred (and selected in operation 305) by the client device 200, operation 309. However, in the example of Fig. 3C, the network node device 210 may fail to receive the first message, in which case operation 309 may fail to happen.

If operation 309 is performed, then at operation 310 the network node device 210 transmits the second message comprising the random access response corresponding to the received random access preamble.

In the example of Fig. 3C, the client device

200 fails to receive the second message comprising the random access response within the given time period at operation 310. Accordingly, the client device 200 performs power ramping, operation 311c. At operation 312c, the client device 200 retransmits the first message with power ramping via the given uplink beam pair for a predetermined amount of times. This amount of times for retransmitting the first message with power ramping via the given uplink beam pair may be configured by the network node device 210.

If the client device 200 still fails to receive the second message comprising the random access response within the given time period, the client device 200 performs a next retransmission of the first message via another uplink beam pair out of the multiple uplink beam pairs, operation 313c.

In the example of Fig. 3C, the client device 200 performs ramping transmission power before beam pair switching for the retransmissions of the first message. Fig. 4C and Fig. 4D further illustrate this.

The diagram 430 of Fig. 4C illustrates the client device 200 selecting two RACH resources and having two beam pairs 431, 432. In this example, the network node device 210 has configured the amount of retransmission as two. Accordingly, the client device 200 may transmit no more than two times before Msgl is transmitted on another beam pair. Accordingly, after the first retransmission, since the client device 200 can transmit no more than two times continuously on the same beam pair, the client device 200 skips the retransmission this time (even though the client device 200 could use the left side Tx beam) . Then, in the second retransmission the beam pair is switched to the other one .

In the example of Fig. 4C, the initial transmission is performed with the UL Tx-Rx beam pair 431 with its power ramping counter value 434 being 0. The first retransmission is performed with the UL Tx-Rx beam pair 431 with its power ramping counter value 434 increased to 1. The second retransmission is performed with the UL Tx-Rx beam pair 432 with its power ramping counter value 434 being 0. The third retransmission is performed with the UL Tx-Rx beam pair 432 with its power ramping counter value 434 increased to 1. The fourth retransmission is performed with the UL Tx-Rx beam pair 431 with its power ramping counter value 434 increased to 2. The fifth retransmission is performed with the UL Tx-Rx beam pair 431 with its power ramping counter value 434 increased to 3.

Herein, when the client device 200 changes its uplink Tx-Rx beam pair, the value of the power ramping counter is changed independent of the power ramping counters for any other uplink beam pairs, and the value of the power ramping counter is based on the previous value of the counter for that same power ramping process. Furthermore, the power ramping process later returns to the first beam pair and continues with the old value of the power ramping counter. The diagram 440 of Fig. 4D illustrates the client device 200 selecting two RACH resources and having two beam pairs 441, 442, similar to Fig. 4C. However, the Rx beam pattern of the two beam pairs 441, 442 at the network node device 210 is different from that in diagram 430 of Fig. 4C. Since the Rx beams at the network node device 210 are different between the initial transmission and the first retransmission, the client device 200 switches to another beam pair in the first retransmission and performs a new power ramping for this new beam pair.

In Fig. 4D, at the network node device 210 side, several time domain contiguous Rx beam sweeping subframes constitute one group of RACH sweeping subframes. In the example of Fig. 4D, more than one preamble can be sent in one group of RACH sweeping sub- frames since it is possible to select multiple uplink beam pairs. More specifically, two preambles can be sent in one group of RACH sweeping subframes, since the Rx beam is changed for two successive (re) transmissions . Hence, there is no need to wait for a new group of RACH sweeping subframes to appear to send the first, third, fifth and seventh retransmission since these retransmissions can be sent in the same group of RACH sweeping subframes as the respective initial transmission, second retransmission, fourth retransmission and sixth retransmission. Hence, the frequency of RACH preamble transmissions can be at least doubled with the embodi ^¬ ment of Fig. 4D. In the example of Fig. 4D, the initial transmission is performed with the UL Tx-Rx beam pair 441 with its power ramping counter value 444 being 0. The first retransmission is performed with the UL Tx-Rx beam pair 442 with its power ramping counter value 444 being 0. The second retransmission is performed with the UL Tx-Rx beam pair 441 with its power ramping counter value 444 increased to 1. The third retransmission is performed with the UL Tx-Rx beam pair 442 with its power ramping counter value 444 increased to 1. The fourth retransmission is performed with the UL Tx-Rx beam pair 441 with its power ramping counter value 444 increased to 2. The fifth retransmission is performed with the UL Tx-Rx beam pair 442 with its power ramping counter value 444 increased to 2. The sixth retransmission is performed with the UL Tx-Rx beam pair 441 with its power ramping counter value 444 increased to 3. Then, the seventh retransmission is performed with the UL Tx-Rx beam pair 442 with its power ramping counter value 444 increased to 3.

In the examples of Fig. 3A to Fig. 3C, a maximum total number may be set for transmissions on all beam pairs. This maximum total number may be configured by the network node device 210 or the maximum total number may be a predefined value.

Furthermore, a maximum total number may be set for transmissions on each beam pair, wherein the maximum total number is configured by the network node device or a predefined value. Again, this maximum total number may be configured by the network node device 210 or the maximum total number may be a predefined value.

In the examples of Fig. 3A to Fig. 3C as well as Fig. 4B and 4D, at least one retransmission may be performed in a single random access beam sweeping procedure of the network device by changing receive beams of the uplink beam pairs for two consecutive preamble transmissions.

The functionality described herein can be performed, at least in part, by one or more computer program product components such as software components. According to an embodiment, the client device 200 and/or network node device 210 comprise a processor configured by the program code when executed to execute the embodiments of the operations and functionality described. Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs) , Program- specific Integrated Circuits (ASICs) , Program-specific Standard Products (ASSPs) , System-on-a-chip systems (SOCs) , Complex Programmable Logic Devices (CPLDs) , and Graphics Processing Units (GPUs) .

Any range or device value given herein may be extended or altered without losing the effect sought. Also any embodiment may be combined with another embodiment unless explicitly disallowed.

Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.

The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought.

The term 'comprising' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this specification .