WO2018143846A1

WO2018143846A1 - Timing-advance handling for separate beam-pair links

Info

Publication number: WO2018143846A1
Application number: PCT/SE2017/050570
Authority: WO
Inventors: Qiang Zhang; Niclas Wiberg; Håkan ANDERSSON; Johan FURUSKOG; Mattias Frenne; John SKÖRDEMAN; Tomas Sundin; Johan KÅREDAL
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-01-31
Filing date: 2017-05-30
Publication date: 2018-08-09

Abstract

Beam-pair link (BPL) uplink timing measurements and timing adjustments are introduced. That is, in some embodiments, separate timing-advance handling for separate BPLs is introduced such that each BPL is operated using a timing advance that matches the transmission conditions and capabilities of the UE. For instance, in some embodiments, for each BPL, the UE stores a distinct uplink (UL) timing-advance value (TAV). Thus, in such embodiments, if, for example, the UE has two monitored BPLs (e.g., one active BPL and one non-active BPL, or two active BPLs), the UE will store two distinct TAVs, one TAV for the first BPL and a separate TAV for the second BPL. Additionally, in some embodiments, in scenarios in which a UE only supports a single UL inverse FFT timing window, all active BPLs for the UE will have the same UL TAV.

Description

TIMING- AD VANCE HANDLING FOR SEPARATE BEAM-PAIR LINKS

TECHNICAL FIELD

[001] Disclosed are embodiments for timing-advance handling for separate beam-pair links (BPLs).

BACKGROUND

[002] The next generation mobile wireless communication system, which is referred to as "5G," will support a diverse set of use cases and a diverse set of deployment scenarios. 5G will encompass an evolution of today's 4G networks and the addition of a new, globally standardized radio-access technology known as "New Radio" (NR).

[003] The diverse set of deployment scenarios includes deployment at both low frequencies (100s of MHz), similar to LTE today, and very high frequencies (mm waves in the tens of GHz). At high frequencies, propagation characteristics make achieving good coverage challenging. One solution to the coverage issue is to employ beamforming (e.g., high-gain beamforming) to achieve satisfactory link budget.

[004] Beamforming is an important technology in future radio communication systems.

It can improve performance both by increasing the received signal strength, thereby improving the coverage, and by reducing unwanted interference, thereby improving the capacity.

Beamforming can be applied both in a transmitter and a receiver.

[005] In a transmitter, beamforming involves configuring the transmitter to transmit the signal in a specific direction (or a few directions) and not in other directions. In a receiver, beamforming involves configuring the receiver to receive signals from a certain direction (or a few directions) and not from other directions. When beamforming is applied in both the transmitter and the receiver for a given communication link, the combination of the beam used by the transmitter to transmit a signal to the receiver and the beam used by the receiver to receive the signal is referred to as a beam-pair link (BPL). Generally, the beamforming gains are related to the widths of the used beams: a relatively narrow beam provides more gain than a wider beam. A BPL can be defined for DL and UL separately or jointly based on reciprocity assumptions. [006] For a more specific description of beamforming, one typically talks about beamforming weights rather than beams. On the transmission side, the signal to be transmitted is multiplied with beamforming weights (e.g., complex constants) before being distributed to the individual antenna elements. There is a separate beamforming weight for each antenna element, which allows maximum freedom in shaping the transmission beam given the fixed antenna array. Correspondingly, on the receiving side, the received signal from each antenna element is multiplied separately with the beamforming weights before the signals are combined. However, in the context of the present text, the description is easier to follow if the somewhat simplified notion of beams, pointing in certain physical directions, is adopted.

[007] Beamforming generally requires some form of beam management, such as beam search, beam refinement, and/or beam tracking, to determine what transmit (Tx) and receive (Rx) beams to use for communication between two units. Typically, the two units are a Transmission and Reception Point (TRP) (e.g., a base station) and a user equipment (UE) (e.g., a device, such as, for example, a smartphone, a sensor, etc., that is capable of wireless communication).

[008] Beam search can involve the transmitter sweeping a signal across several beams

(i.e., transmitting a signal, such as a reference signal, multiple times using different Tx beams), to allow a receiver in an unknown direction to receive the signal. Beam search can also involve the receiver scanning across several receive beams, thereby being able to receive a signal from an initially unknown direction. Beam search typically also involves the receiver sending a message to a transmitter to indicate which transmit beam or beams are best suited for

transmission to that receiver.

[009] Beam refinement is applied when a working beam or beam pair is already selected. Beam refinement is to improve an already selected beam, for instance changing its beamforming weights to obtain a narrower beam that provides a better gain.

[0010] Beam tracking is process that is used to update the selected beams, i.e., to replace the Tx or Rx beam in an existing BPL when the conditions change (e.g., due to mobility). Beam refinement and tracking are typically performed by temporarily evaluating a different beam than the one that is currently used for communication, and switching to that beam if it is deemed better than the current beam. [0011] Beam search can take a considerable amount of time when there are many beams to search for on both the transmitter and receiver side, and communication is typically not possible during this search time. Beam refinement and tracking, on the other hand, are usually ongoing activities that cause little or no disturbance to ongoing communication.

SUMMARY

[0012] Networks often transmit reference signals (e.g., CSI-RS, PSS, SSS, PBCH) to support beam management (e.g. by sweeping across several transmit beams as describe above). Such a reference signal is referred to as beam reference signal (BRS) or a mobility reference signal (MRS). Some aspects of beam management can be performed by a UE with little or no explicit involvement from the network, since the UE can assume that the network is transmitting the BRS periodically or continuously. For instance, UEs typically perform beam search as part of the system-acquisition procedure, resulting in the selection of a UE Rx beam such that by using this beam it can sufficiently well receive BRS transmitted on a certain network beam. Then the UE performs a random-access transmission using a selected Tx beam and using a transmission resource (time and/or frequency) where the UE expects the network to be able to receive random-access transmissions using that beam. UEs often continue to receive BRS even when communication is ongoing - this facilitates beam search, beam refinement and beam tracking.

[0013] Many radio communication systems include some kind of radio-link supervision, whereby the quality of the communication link is regularly checked, and some action is taken in case the quality is unacceptable or the communication is lost. Radio-link supervision often involves a receiver checking the presence and/or quality of a sync signal or a reference signal. It can also involve monitoring the number of retransmissions in a retransmission protocol, and monitoring the time it takes to receive a response to an earlier transmitted request message. In case any of these checks indicate a severe problem, the device often declares a radio-link failure and initiates some action. In case of a network node having lost communication with a UE, the action can involve releasing some or all network resources related to that UE. In case of a UE having lost communication with a network, the action can involve searching for sync and reference signals from the network and, in case such signals are found, attempting to access the network again. In a beamforming system, this typically involves beam search. [0014] In addition, networks schedule and transmit UE- specific reference signals that, among other things, can be used for beam searching, beam tracking, and beam refinement. Such signals are referred to here as beam-refinement reference signals (BRRS). An example of a UE- specific reference signal is the channel-state information reference signal (CSI-RS). This is a reference signal scheduled by the network for one (or possibly, several) specific UE (or UEs) with the intention of providing measurement opportunities in the UE such that more detailed channel knowledge may be obtained and reported back to the network.

[0015] Further, networks (e.g., TRPs) may configure UEs to periodically transmit uplink

(UL) reference signals, which are known as sounding reference signals (SRS).

[0016] To sustain a transmission link between the network and the UE over time-varying conditions (e.g. due to mobility), UEs typically consider several possible BPLs for which the beams are tracked and refined. Such BPLs that are identified jointly by the network and the UE are here referred to as monitored BPLs.

[0017] The monitored BPLs (e.g., active and non-active BPLs) can be tagged with an identifier. This tag could for example be 2 bits, allowing for 4 BPLs being identified.

[0018] In some scenarios, UE-specific CSI-RS is used for beam management and aperiodic measurements are triggered by the network. The CSI-RS can be used to initiate and or refine the active and monitored BPLs. The UE can report which TRP Tx beam it prefers for each measurement and store the preferred Rx processing configuration (such as Rx beam) for each Tx beam. Hence, the Tx-Rx beam pair is a BPL.

[0019] Out of the monitored BPLs, the network and UE agree to use at least one BPL for data and control channel reception and transmission (here referred to as the "active" BPL). Depending on its capabilities, a UE can support one or more active BPLs. The monitored BPLs that are not used as an active BPL are referred to as back-up (or non-active) BPLs. Whether two BPLs can be simultaneously active or not depends on the UE's implementation. If the UE-side beams associated with each BPL are realized using the same processing components such as antenna panels, analog and/or digital circuitry, software units, etc., the UE may not be able to transmit and receive using those UE beams simultaneously. If that is the case, the BPLs are regarded as incompatible. Whether BPLs are compatible or not has to be known by the network, since it typically selects which ones to be active or non-active. This is solved during the initialization of the BPL based on a compatibility indication from the UE to the network.

[0020] Tracking a BPL implies beam tracking and/or refinement at the network as well as the UE. To track a monitored BPL (active or non-active) there must be some transmissions on which to measure and evaluate the link quality. In DL, the more persistent BRS could enable tracking of the DL TX beam and, more slowly, of the DL RX beam. For faster DL RX beam tracking scheduled BRRS (e.g., CSI-RS) can be used. In the event of DL/UL reciprocity, the BRS may then suffice to track a BPL and no UL transmissions are needed. In this case, the BPL is the same for UL and DL. In a scenario where DL/UL reciprocity does not hold, the BPL tracking requires UL transmissions (e.g., SRSs) to maintain the BPL for the UL.

[0021] The main-candidate duplex scheme envisioned for NR is dynamic time-division duplex (TDD), meaning that the transmission direction, whether it is DL or UL, is dynamically scheduled. This makes the use of periodically scheduled reference signals less dependable since they can only be transmitted if the direction of the duplex scheme happens to agree with the scheduled reference signal for a given transmission-time interval (TTI) (e.g., an LTE subframe, an NR slot, etc.).

[0022] Both LTE and the coming 5G wireless communication system are based on orthogonal frequency-division multiplexing (OFDM), which implies that a transmission has to be received within a Fast-Fourier Transform (FFT) window of the receiver to maintain the orthogonal properties of the OFDM waveform. In the downlink, the UE monitors the OFDM symbol timing based on synchronization and reference signals and adjusts its FFT timing correspondingly. In the uplink, the network (e.g., TRP) monitors the OFDM symbol timing. Transmissions from multiple UEs need to arrive approximately time-aligned at the TRP to be properly received within the receiver FFT timing window. The network determines the required timing correction for each UE. If the timing of a specific UE needs correction, the network issues a timing-advance (TA) command on the DL data channel for this specific UE, typically a MAC CE, instructing the UE to delay or advance its timing for uplink transmission. Upon reception of the TA command, the UE shall adjust uplink transmission timing for the UL data channel, UL control channel, and SRS based on the received timing-advance command. [0023] The uplink transmission timing for the UL data channel, the UL control channel, and the SRS is based on a UE-stored timing-advance value ( N_TA or TAV) which indicates the offset between the start of a received downlink TTI and a transmitted uplink TTI. The uplink timing advance, estimated based on those channels or signals and referred to as T_R , is the relative timing-advance value in reference to the current N_TA used by the UE. If the timing- advance command received contains a relative value T_R , the UE updates its stored timing- advance value as follows: N_{TA new} = N_TA,oid + T_R■

[0024] The physical random-access channel (PRACH) is transmitted with N_TA = 0 , so the uplink timing advance based on the estimation on the PRACH is the absolute timing- advance value T_A . If the timing-advance command received contains an absolute value T_A , the UE updates its timing-advance value to N_TA = T_A .

[0025] The existing solution for uplink transmission timing is unable to account for the different propagation conditions that may occur for different combinations of BPLs used, either simultaneously during one TTI transmission-time interval or when switching between BPLs in consecutive transmission-time intervals. Additionally, for a UE with a single IFFT time window for UL transmissions, the network may have difficulties receiving on multiple BPLs when the propagation delay difference is too large between the BPLs. And finally, when switching to a new BPL, the existing solution uses the same uplink transmission timing for the new BPL. The switching can fail if the propagation-delay difference is too large.

[0026] Accordingly, this disclosure describes embodiments for reducing the impact of one or more of the above described problems. Specifically, this disclosure describes

embodiments in which per BPL uplink timing measurements and timing adjustments are introduced. That is, in some embodiments, separate timing-advance handling for separate BPLs is introduced such that each BPL is operated using a timing advance that matches the transmission conditions and capabilities of the UE. For instance, in some embodiments, for each BPL, the UE stores a distinct uplink (UL) timing-advance value (TAV). Thus, in such embodiments, if, for example, the UE has two monitored BPLs (e.g., one active BPL and one non-active BPL, or two active BPLs), the UE will store two distinct TAVs, one TAV for the first BPL and a separate TAV for the second BPL. Additionally, in some embodiments, in scenarios in which a UE only supports a single UL inverse FFT (IFFT) timing window, all active BPLs for the UE will have the same UL TAV.

[0027] For example, in aspect there is provided a method performed by a UE for separate timing-advance handling for separate beam-pair links (BPLs). The method includes the UE storing a first UE timing-advance value (TAV) for use with a first UL BPL. The method also includes the UE storing a second UE TAV for use with a second UL BPL. The second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL.

[0028] In some embodiments, the method also includes the UE receiving a first network

TAV; and the UE adjusting the first UE TAV based on the first network TAV, but not adjusting the second UE TAV based on the first network TAV. The method may further include the UE receiving a second network TAV; and the UE adjusting the second UE TAV based on the second network TAV, but not adjusting the first UE TAV based on the second network TAV. In some embodiments, the first network TAV is a relative TAV transmitted to the UE from a transmission and reception point (TRP), adjusting the first UE TAV based on the first network TAV comprises calculating TAVuel = TAVuel + Tr, wherein TAVuel is the first UE TAV and Tr is the relative TAV, the second network TAV is an absolute TAV transmitted to the UE from a TRP, and adjusting the second UE TAV based on the second network TAV comprises calculating TAVue2 = Ta, wherein TAVue2 is the second UE TAV and Ta is the absolute TAV.

[0029] In some embodiments, receiving the first network TAV comprises receiving a timing-advance, TA, command comprising the first network TAV and further comprising information indicating that the first network TAV is for use with the first UL BPL.

[0030] In some embodiments, receiving the first network TAV comprises receiving a timing-advance, TA, command on a DL BPL identified by BPL index n, and the first UL BPL is also identified by BPL index n.

[0031] In some embodiments, the method also includes the UE receiving a first network

TAV for the first UL BPL; the UE receiving a second network TAV for the second UL BPL; the UE calculating ΔΤ=Τ A Vn 1 -TA Vn2, wherein TAVnl is the first network TAV and TAVn2 is the second network TAV; and the UE determining whether ΔΤ is not less than a threshold. In such an embodiments, the UE may only support UL transmission with a single Inverse Fast Fourier Transform window. In some embodiments, the method further includes the UE, in response to determining that ΔΤ is greater than the threshold, transmitting to a TRP a message indicating that ΔΤ is greater than the threshold. In some embodiments, the method further includes the UE releasing the second UL BPL in response to determining that ΔΤ is greater than the threshold.

[0032] In some embodiments, the first UL BPL and the second UL BPL are active at the same time.

[0033] In another aspect there is provided a method performed by a TRP for separate timing-advance handling for separate BPLs. The method includes the TRP sending to a UE a first TAV for adjusting a first UE-stored TAV associated with a first UL BPL. The method further includes the TRP sending to the UE a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL. The second UE-stored TAV is distinct from the first UE-stored TAV, and the second UL BPL is distinct from the first UL BPL.

[0034] In some embodiments, prior to transmitting the first and second TAVs, the TRP: generates a first initial TAV associated with the first UL BPL based on a Physical Random Access Channel transmission from the UE; and transmits to the UE the initial TAV, wherein when the UE stores the initial TAV the initial TAV becomes the first UE-stored TAV.

[0035] In some embodiments, the first TAV is one of: a relative TAV and an absolute

TAV. In embodiments in which the first TAV is a relative TAV, the TRP generates the relative TAV based on one of: 1) a timing estimation of a UE- specific demodulation reference signal transmitted by the UE on the first UL BPL and 2) a timing estimation of a UL sounding reference signal, SRS, transmitted by the UE on the first UL BPL.

[0036] In embodiments in which the first TAV is an absolute TAV, the TRP orders the

UE to perform a PRACH transmission on the first UL BPL, the TRP receives the PRACH transmission, and the TRP generates the absolute TAV based on the received PRACH

transmission.

[0037] In some embodiments, sending to the UE the first TAV for adjusting the first UE- stored TAV associated with the first UL BPL comprises the TRP sending the first TAV to the UE on a first DL BPL associated with a certain index and the first UL BPL is also associated with said certain index.

[0038] In some embodiments, sending to the UE the first TAV for adjusting the first UE- stored TAV associated with the first UL BPL comprises the TRP sending to the UE a timing- advance, TA, command comprising the first TAV and further comprising information indicating that the first TAV is for use with the first UL BPL.

[0039] In another aspect there is a provided another method performed by a TRP for timing-advance handling for separate BPLs. The method includes the TRP determining a first timing-advance value (TAV1) associated with a first UL BPL established with a UE. The method also includes the TRP determining a second timing-advance value (TAV2) associated with a second UL BPL established with the UE. The method further includes the TRP determining ΔΤ, wherein ΔΤ is absolute value of, TAV1-TAV2. The method further includes the TRP comparing ΔΤ with a threshold. And the method also includes the TRP performing one of: 1) in response to determining that ΔΤ is less than the threshold, generating the same determined timing-advance adjustment to the first UL BPL and the second UL BPL, wherein the determined timing-advance adjustment is equal to the minimum of TAV1 and TAV2, and 2) in response to determining that ΔΤ is greater than the threshold, deactivating one of the first UL BPL and the second UL BPL.

[0040] An advantage of introducing per BPL timing measurement processes is that it enables optimized UL timing-advance adjustments for UL transmissions when, for example, several active BPLs are used simultaneously during one transmission-time interval.

Additionally, BPLs with large propagation delay differences will not be activated at the same time if the UE supports only a single UL IFFT timing window.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0042] FIG. 1 illustrates the use of BPLs for communications between a TRP and a UE.

[0043] FIG. 2 is a flow chart illustrating a process according to one embodiment. [0044] FIG. 3 is a flow chart illustrating a process according to one embodiment.

[0045] FIG. 4 is a flow chart illustrating a process according to one embodiment.

[0046] FIG. 5 is a block diagram of a TRP according to some embodiments.

[0047] FIG. 6 is a block diagram of a UE according to some embodiments.

[0048] FIG. 7 is a diagram showing functional modules of a UE according to some embodiments.

[0049] FIG. 8 is a diagram showing functional modules of a TRP according to some embodiments.

[0050] FIG. 9 is a diagram showing functional modules of a TRP according to some embodiments.

DETAILED DESCRIPTION

[0051] In FIG. 1 there is shown a TRP 150 (e.g., a base station) utilizing a first TRP Rx beam 102 to receive signals from a UE 101 when UE 101 transmits the signals on a first UE Tx beam 106 and further utilizing a second TRP Rx beam 103 to receive signals from UE 101 when UE 101 transmits the signals on a second UE Tx beam 107. Accordingly, in this example, TRP 105 and UE 101 communicate using two UL BPLs - a first UL BPL that consists of beams 102 and 106 and a second UL BPL that consists of beams 103 and 107. While FIG. 1 illustrates a single TRP communicating with UE 101, in other embodiments two or more TRPs may be communicating with UE 101, wherein one of the TRPs uses an active BPL to communicate with UE 101 and another of the TRPs uses another active BPL to communicate with UE 101.

[0052] As mentioned above, the existing solution for uplink transmission timing is unable to account for the different propagation conditions that may occur for different BPLs. Accordingly, this disclosure describes embodiments of a wireless communication system in which per BPL timing measurements and adjustments are introduced.

[0053] For a BPL with index n (i.e., BPLn), let N_{TA n} denote the timing-advance value used for the BPLn; let T_{R n} denote the relative timing advance for BPLn; and let T_{A n} denote the absolute timing advance for BPLn. [0054] Uplink timing-advance estimation

[0055] In one embodiment, the initial UL timing-advance value N_{TA n} for BPLn is based on the timing estimation on the PRACH channel transmitted during the random-access procedure.

[0056] In one embodiment, the relative uplink timing advance T_{R n} of BPLn is based on the timing estimation on the UE-specific demodulation reference signal (DMRS) of the data channel or the control channel transmitted in UL on the active BPL. In another embodiment, T_{R n} is based on the timing estimation on the scheduled UL sounding reference signal transmitted on the BPL. In another embodiment, the network (e.g., TRP 150) orders UE 101 to transmit PRACH on BPLn, so the absolute uplink timing advance T_{A n} can be estimated.

[0057] In another embodiment, the network (e.g., TRP 105) sends a command to UE

101 to activate BPLn, the UE 101 then acknowledges the command by transmitting using the PRACH channel on the newly activated BPL (i.e., BPLn). The absolute uplink timing advance T_{A n} of the BPL can then be estimated.

[0058] In another embodiment, the cellular system is comprised of several component carriers and the network measures the uplink timing of the active/monitored BPL on one of the component carriers. Alternatively, the network measures uplink timing on several or all component carriers.

[0059] Uplink timing-advance adjustments and beam management

[0060] In some embodiments, when the UE 101 is scheduled for an UL transmission on a BPL, UL timing-advance (TA) commands are received based on the uplink timing measured on the BPL. The timing advance received in the TA command for the BPLn can be a relative value, T_{R n} , or an absolute value, T_{A n} .

[0061] In one embodiment, the TA command is received on one active BPL with index n = N_x in the DL and the UL timing-advance adjustment is applied to the same active BPL with index n = N_l . [0062] In another embodiment, the TA command is received on one active BPL with index n = N_l and the UL timing-advance adjustment is applied to one of the other monitored or active BPLs with index n≠ N_l .

[0063] In another embodiment, the TA command is received on one active BPL with index n = N_l and the UL timing-advance adjustment is applied to several or all monitored and/or active BPLs with indices n = N_l, N₂ ,...

[0064] In another embodiment, the TA command is received on one component carrier with index c = C_x and the UL timing-advance adjustment is applied to several or all component carriers.

[0065] In another embodiment, multiple TA commands are received on one or more active BPLs, one TA command per active or monitored BPL. The TA command for BPL with index n = N_l can be received on BPL with index n = N_l or n≠ N_l .

[0066] Let T_m denote uplink timing advance based on the timing estimation on a first

BPL with index n = N_l , T_N2 denote uplink timing advance based on the timing estimation on a second BPL with index n = N₂ . Let Δ T be the difference between T_m and T_N2 . Here T_N1 and

T_N2 are the same type of timing advance value, either both of them are relative values or both of them are absolute values.

[0067] Some UEs support UL transmission with multiple IFFT time windows simultaneously. In such a scenario, in some embodiments, the network (e.g., TRP 150) sends one TA command for each BPL. The UE 101 applies T_N1 to the BPL with index n = N_l , T_N2 to

BPL with index n = N₂ and so forth. As an example, if UE 101 has two monitored BPLs (i.e., a first BPL (BPLl) and a second BPL (BPL2)), then UE 101 will store a first TAV (TAV1) that is associated with BPLl and will store another TAV (TAV2) that is associated with BPL2; and, when UE 101 receives a TA command with a timing-adjustment (relative or absolute) for BPLl, UE 101 will adjust TAV1 based on the timing-adjustment for BPLl, and, likewise, when UE 101 receives a timing-adjustment (relative or absolute) for BPL2, UE 101 will adjust TAV2 based on the timing-adjustment for BPL2.

[0068] Other UEs only support UL transmission with a single IFFT time window at the same transmission interval. The network sends one TA command for each BPL, the UE applies T_m to BPL with index n = N_l at the first transmission interval, and applies T_N2 to the BPL with index n = N₂ at the second transmission interval. If both BPLs are active, the UE uses the same N_TA for all active BPLs. If Δ T is below a certain threshold, the network sends one

TA command for all active BPLs with a timing-advance value equal to m (T_m,T_N2) , and the UE applies this timing-advance adjustment to all active BPLs.

[0069] In another embodiment, Δ T is above a threshold and both BPLs are active, then the network determines to deactivate one of the active BPLs.

[0070] In another embodiment, the network sends one TA command per active BPL but the UE only supports UL transmission with a single IFFT time window. The UE then applies the timing-advance adjustment value equal to min(T_m,T_N2) to all active BPLs.

[0071] In another embodiment, the network sends one TA command per active BPL but the UE only supports UL transmission with a single IFFT time window. If Δ T is above a threshold, the UE sends an indication message to the network, and the network determines to deactivate one of the active BPLs.

[0072] In another embodiment, Δ T is above a threshold but the UE only supports UL transmission with a single IFFT time window. The BPL with index n = N₂ is a monitored BPL. The network does not activate BPL with index n = N₂ when BPL with index n = N_l active. Alternatively, the network can release the BPL with index n = N₂ .

[0073] In another embodiment, Δ T is above a threshold but the UE only supports UL transmission with a single IFFT time window. Both BPLs are monitored BPL. In this case, the network only activates one of the monitored BPLs. [0074] FIG. 2 is a flow chart illustrating a process 200, according to some embodiments, for separate timing-advance handling for separate beam-pair links (BPLs).

Process 200 may begin in step 202 in which UE 101 stores a first UE timing-advance value (TAV) for use with a first UL BPL. In step 204, UE 101 stores a second UE TAV for use with a second UL BPL. The second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL. In this way, UE can have separate timing adjustments for separate BPLs.

[0075] In some embodiments, the process also includes the UE receiving a first network

TAV (e.g.,, a timing-adjustment value included in the TA command transmitted by the network) (step 206); and the UE adjusting the stored first UE TAV based on the first network TAV, but does not adjust the stored second UE TAV based on the first network TAV (step 208). The process may further include the UE receiving a second network TAV (step 210); and the UE adjusting the stored second UE TAV based on the second network TAV, but not adjusting the stored first UE TAV based on the second network TAV (step 212). In this way, the stored UE TAVs are separately handled.

[0076] In some embodiments, the first network TAV is a relative TAV transmitted to the

UE from a TRP. In such an embodiment, adjusting the first UE TAV based on the first network TAV comprises calculating TAVuel = TAVuel + Tr, wherein TAVuel is the first UE TAV and Tr is the relative TAV.

[0077] In some embodiments, the second network TAV is an absolute TAV transmitted to the UE from a TRP, and the step of adjusting the second UE TAV based on the second network TAV comprises setting TAVue2 = Ta, wherein TAVue2 is the second UE TAV and Ta is the absolute TAV.

[0078] In some embodiments, receiving the first network TAV comprises receiving a timing-advance (TA) command comprising the first network TAV and further comprising information indicating that the first network TAV is for use with the first UL BPL.

[0079] In some embodiments, receiving the first network TAV comprises receiving a timing-advance (TA) command on a DL BPL identified by BPL index n, and the first UL BPL is also identified by BPL index n. [0080] In some embodiments, the UE only supports UL transmission with a single

Inverse Fast Fourier Transform (IFFT) window. In such embodiments, the process may further include: the UE receiving a first network TAV for the first UL BPL; the UE receiving a second network TAV for the second UL BPL; the UE calculating ΔΤ = (TAVnl - TAVn2), wherein TAVnl is the first network TAV and TAVn2 is the second network TAV; the UE determining whether ΔΤ is not less than a threshold; and in response to determining that ΔΤ is greater than the threshold, the UE may a) transmit to a TRP a message indicating that ΔΤ is greater than the threshold and/or release one of the first UL BPL and the second UL BPL.

[0081] FIG. 3 is a flow chart illustrating a process 300, according to some

embodiments, for separate timing-advance handling for separate beam-pair links (BPLs).

Process 300 may begin in step 302 in which TRP 150 sends to UE 101 a first timing-advance value (TAV) (a relative TAV or absolute TAV) for adjusting a first UE-stored TAV associated with a first UL BPL. In step 304, the TRP sends to the UE a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL. The second UE-stored TAV is distinct from the first UE-stored TAV, and the second UL BPL is distinct from the first UL BPL.

[0082] In some embodiments, prior to transmitting the first and second TAVs, the TRP:

1) generates a first initial TAV associated with the first UL BPL based on a transmission from the UE (e.g., a Physical Random-Access Channel (PRACH) transmission) (step 301a) and 2) transmits to the UE the initial TAV (step 301b), wherein when the UE stores the initial TAV the initial TAV becomes the first UE-stored TAV. In some embodiments, the first initial TAV is based on a the receipt of a random-access preamble transmitted by the UE on the PRACH.

[0083] In some embodiments, the first TAV is a relative TAV, and the TRP generates the relative TAV based on one of: 1) a timing estimation of a UE-specific demodulation reference signal transmitted by the UE on the first UL BPL and 2) a timing estimation of a UL sounding reference signal (SRS) transmitted by the UE on the first UL BPL.

[0084] In other embodiments, the first TAV is an absolute TAV, the TRP orders the UE to perform a PRACH transmission on the first UL BPL, the TRP receives the PRACH transmission, and the TRP generates the absolute TAV based on the received PRACH transmission. [0085] In some embodiments, the TRP sends to the UE the first TAV for adjusting the first UE-stored TAV associated with the first UL BPL by sending the first TAV to the UE on a first DL BPL associated with a certain index, and the first UL BPL is also associated with said certain index.

[0086] In some embodiments, the TRP sends to the UE the first TAV for adjusting the first UE-stored TAV associated with the first UL BPL by sending to the UE a timing-advance (TA) command comprising the first TAV and further comprising information indicating that the first TAV is for use with the first UL BPL.

[0087] FIG. 4 is a flow chart illustrating a process 400, according to some

embodiments, for timing-advance handling for separate beam-pair links (BPLs). Process 400 may begin in step 402 in which the TRP determines a first timing-advance value (TAV1) associated with a first UL BPL established with a UE. In step 404, the TRP determines a second timing-advance value (TAV2) associated with a second UL BPL established with the UE. In step 406, the TRP determines ΔΤ, wherein ΔΤ is absolute value of (TAV1-TAV2).

[0088] In step 408, the TRP compares ΔΤ with a threshold.

[0089] In response to determining that ΔΤ is less than the threshold, the TRP generates the same determined timing-advance adjustment to the first UL BPL and the second UL BPL, wherein the determined timing-advance adjustment is equal to the minimum of TAV1 and TAV2 (i.e., the determined timing-advance adjustment = min(TAVl, TAV2)) (step 410).

[0090] In response to determining that ΔΤ is greater than the threshold, the TRP deactivates one of the first UL BPL and the second UL BPL (step 412).

[0091] FIG. 5 is a block diagram of TRP 150 according to some embodiments. As shown in FIG. 5, TRP 150 may comprise: a data-processing system (DPS) 502, which may include one or more processors (P) 555 (e.g., a general-purpose microprocessor and/or one or more other processors, such as an application- specific integrated circuit (ASIC), field- programmable gate arrays (FPGAs), and the like); a transmitter 505 and a receiver 506 coupled to an antenna 522 for use in wirelessly communicating with a UE; a network interface 548 for use in connecting TRP 150 to a network 110 (e.g., an Internet Protocol (IP) network) so that TRP 150 can communicate with other devices connected to network 110; and local storage unit (a.k.a., "data storage system") 508, which may include one or more non-volatile storage devices and/or one or more volatile storage devices (e.g., random-access memory (RAM)). In embodiments where TRP 150 includes a general-purpose microprocessor, a computer-program product (CPP) 541 may be provided. CPP 541 includes a computer-readable medium (CRM) 542 storing a computer program (CP) 543 comprising computer-readable instructions (CRI) (a.k.a., "program code") 544. CRM 542 may be a non-transitory computer-readable medium, such as, but not limited, to magnetic media (e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g., random-access memory), and the like. In some embodiments, the CRI 544 of computer program 543 is configured such that when executed by data-processing system 502, the CRI causes TRP 150 to perform steps described above (e.g., steps described above with reference to the flow charts). In other embodiments, TRP 150 may be configured to perform steps described herein without the need for code. That is, for example, data-processing system 502 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0092] FIG. 6 is a block diagram of a UE 101 according to some embodiments. As shown in FIG. 6, UE 101 may comprise: a data-processing system (DPS) 602, which may include one or more processors 655 (e.g., a general-purpose microprocessor and/or one or more other processors, such as an application-specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); a transmitter 605 and a receiver 606 coupled to an antenna 622 for use in wirelessly communicating with a radio-access network (RAN) node (e.g., a TRP); and local storage unit (a.k.a., "data storage system") 612, which may include one or more nonvolatile storage devices and/or one or more volatile storage devices (e.g., random-access memory (RAM)). In embodiments where UE 101 includes a general-purpose microprocessor, a computer-program product (CPP) 641 may be provided. CPP 641 includes a computer-readable medium (CRM) 642 storing a computer program (CP) 643 comprising computer-readable instructions (CRI) (a.k.a., "program code") 644. CRM 642 may be a non-transitory computer- readable medium, such as, but not limited, to magnetic media (e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g., random-access memory), and the like. In some

embodiments, the CRI 644 of computer program 643 is configured such that when executed by data-processing system 602, the CRI causes UE 101 to perform steps described above (e.g., steps described above with reference to the flow charts). In other embodiments, UE 101 may be configured to perform steps described herein without the need for code. That is, for example, data-processing system 602 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0093] FIG. 7 is a diagram showing functional modules of UE 101 according to some embodiments. In the embodiment shown, UE 101 includes: a TAV- storing module 702 for storing: 1) a first UE TAV for use with a first UL BPL and 2) a second UE TAV for use with a second UL BPL, wherein the second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL.

[0094] FIG. 8 is a diagram showing functional modules of TRP 150 according to some embodiments. In the embodiment shown, TRP 150 includes: a TAV- sending module 802 for sending to a UE: 1) a first timing-advance value (TAV) for adjusting a first UE-stored TAV associated with a first UL BPL and 2) a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL, wherein the second UE-stored TAV is distinct from the first UE-stored TAV, and the second UL BPL is distinct from the first UL BPL.

[0095] FIG. 9 is a diagram showing functional modules of TRP 150 according to some embodiments. In the embodiment shown, TRP 150 includes: a determining module 902 configured to: determine a first timing-advance value (TAV1) associated with a first UL BPL established with a UE; determine a second timing-advance value (TAV2) associated with a second UL BPL established with the UE; and determine ΔΤ, wherein ΔΤ is the absolute value of (TAV1-TAV2); a comparing module 904 configured to compare ΔΤ with a threshold; a generating module 906 configured to generate the same determined timing-advance adjustment to the first UL BPL and the second UL BPL in response to determining that ΔΤ is less than the threshold, wherein the determined timing-advance adjustment is equal to the minimum of TAV1 and TAV2 (i.e., the determined timing-advance adjustment = min(TAVl, TAV2)), and a deactivating module 908 configured to deactivate one of the first UL BPL and the second UL BPL in response to determining that ΔΤ is greater than the threshold.

[0096] While various embodiments of the present disclosure are described herein

(including the appendices, if any), it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0097] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[0098] ABBREVIATIONS

[0099] 5G Fifth-Generation Mobile Radio Access

[00100] BBU Base-Band Unit

[00101] BLER Block-Error Rate

[00102] BPL Beam-Pair Link

[00103] BRRS Beam-Refinement Reference Signal

[00104] BRS Beam-Reference Signal

[00105] CE Control Element

[00106] CSI-RS Channel- State Information Reference Signal

[00107] DCI Downlink Control Information (message)

[00108] eNB enhanced Node B (i.e., Base Station)

[00109] HARQ Hybrid Automatic Repeat reQuest

[00110] LTE Long-Term Evolution

[00111] MAC Medium- Access Control

[00112] NR New Radio

[00113] PBCH Physical Broadcast Channel

[00114] PDCCH Physical Downlink Control Channel

[00115] PSS Primary Synchronization Signal

[00116] RRC Radio-Resource Control

[00117] RSRP Reference Signal Received Power

[00118] Rx Receiver

[00119] SRS Sounding Reference Signal [00120] SSS Secondary Synchronization Signal

[00121] Tx Transmitter

[00122] TRP Transmission and Reception Point

Claims

CLAIMS:

1. A method (200) for separate timing-advance handling for separate beam-pair links, BPLs, the method comprising:

a user equipment, UE (101), storing a first UE timing-advance value, TAV, for use with a first UL BPL; and

the UE storing a second UE TAV for use with a second UL BPL, wherein the second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL.

2. The method of claim 1, further comprising:

the UE receiving a first network TAV; and

the UE adjusting the first UE TAV based on the first network TAV, but not adjusting the second UE TAV based on the first network TAV.

3. The method of claim 2, further comprising:

the UE receiving a second network TAV; and

the UE adjusting the second UE TAV based on the second network TAV, but not adjusting the first UE TAV based on the second network TAV.

4. The method of claim 3, wherein

the first network TAV is a relative TAV transmitted to the UE from a transmission and reception point, TRP,

adjusting the first UE TAV based on the first network TAV comprises calculating TAVuel = TAVuel + Tr, wherein TAVuel is the first UE TAV and Tr is the relative TAV, the second network TAV is an absolute TAV transmitted to the UE from a TRP, and adjusting the second UE TAV based on the second network TAV comprises calculating TAVue2 = Ta, wherein TAVue2 is the second UE TAV and Ta is the absolute TAV.

5. The method of any one of claims 1-4, wherein receiving the first network TAV comprises receiving a timing-advance, TA, command comprising the first network TAV and further comprising information indicating that the first network TAV is for use with the first UL BPL.

6. The method of any one of claims 1-4, wherein

receiving the first network TAV comprises receiving a timing-advance, TA, command on a DL BPL identified by BPL index n, and

the first UL BPL is also identified by BPL index n.

7. The method of any one of claims 1-6, further comprising:

the UE receiving a first network TAV for the first UL BPL;

the UE receiving a second network TAV for the second UL BPL;

the UE calculating AT=TAVnl-TAVn2, wherein TAVnl is the first network TAV and TAVn2 is the second network TAV; and

the UE determining whether ΔΤ is not less than a threshold.

8. The method of claim 7, wherein

the UE only supports UL transmission with a single Inverse Fast Fourier Transform window, and

the method further comprises the UE, in response to determining that ΔΤ is greater than the threshold, transmitting to a transmission and reception point, TRP, a message indicating that ΔΤ is greater than the threshold.

9. The method of claim 7, wherein

the method further comprises the UE, in response to determining that ΔΤ is greater than the threshold, releasing the second UL BPL.

10. The method of any one of claims 1-9, wherein the first UL BPL and the second UL BPL are active at the same time.

11. A method (300) for separate timing-advance handling for separate beam-pair links, BPLs, the method comprising:

a transmission and reception point, TRP, (150) sending to a UE (101) a first timing- advance value, TAV, for adjusting a first UE-stored TAV associated with a first UL BPL; and the TRP sending to the UE a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL, wherein

the second UE-stored TAV is distinct from the first UE-stored TAV, and

the second UL BPL is distinct from the first UL BPL.

12. The method of claim 11, wherein prior to transmitting the first and second TAVs, the

TRP:

generates a first initial TAV associated with the first UL BPL based on a Physical Random Access Channel, PRACH, transmission from the UE; and

transmits to the UE the initial TAV, wherein when the UE stores the initial TAV the initial TAV becomes the first UE-stored TAV.

13. The method of claim 11 or 12, wherein the first TAV is one of: a relative TAV and an absolute TAV.

14. The method of claim 13, wherein

the first TAV is a relative TAV, and

the TRP generates the relative TAV based on one of: 1) a timing estimation of a UE- specific demodulation reference signal transmitted by the UE on the first UL BPL and 2) a timing estimation of a UL sounding reference signal, SRS, transmitted by the UE on the first UL BPL.

15. The method of claim 13, wherein the first TAV is an absolute TAV,

the TRP orders the UE to perform a PRACH transmission on the first UL BPL, the TRP receives the PRACH transmission, and

the TRP generates the absolute TAV based on the received PRACH transmission.

16. The method of any one of claims 11-15, wherein sending to the UE the first TAV for adjusting the first UE-stored TAV associated with the first UL BPL comprises the TRP sending the first TAV to the UE on a first DL BPL associated with a certain index and the first UL BPL is also associated with said certain index.

17. The method of any one of claims 11-15, wherein sending to the UE the first TAV for adjusting the first UE-stored TAV associated with the first UL BPL comprises the TRP sending to the UE a timing-advance, TA, command comprising the first TAV and further comprising information indicating that the first TAV is for use with the first UL BPL.

18. A method (400) for timing-advance handling for separate beam-pair links, BPLs, the method comprising:

a transmission and reception point, TRP (150), determining a first timing-advance value, TAV1, associated with a first UL BPL established with a UE;

the TRP determining a second timing-advance value, TAV2, associated with a second UL BPL established with the UE;

the TRP determining ΔΤ, wherein ΔΤ is absolute value of, TAV1-TAV2;

the TRP comparing ΔΤ with a threshold; and

the TRP performing one of:

1) in response to determining that ΔΤ is less than the threshold, generating the same determined timing-advance adjustment to the first UL BPL and the second UL BPL, wherein the determined timing-advance adjustment is equal to the minimum of TAV1 and TAV2, and

2) in response to determining that ΔΤ is greater than the threshold, deactivating one of the first UL BPL and the second UL BPL.

19. A user equipment, UE (101), the UE being adapted to:

store a first UE timing-advance value, TAV, for use with a first UL BPL; and

store a second UE TAV for use with a second UL BPL, wherein the second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL.

20. The UE of claim 19, wherein the UE is further adapted to perform the method of any one of claims 2-10.

21. A user equipment, UE (101), the UE comprising:

a TAV-storing module (702) for storing: 1) a first UE TAV for use with a first UL BPL and 2) a second UE TAV for use with a second UL BPL, wherein the second UE TAV is distinct from the first UE TAV and the second UL BPL is distinct from the first UL BPL.

22. The UE of claim 21, wherein the UE further comprises modules for performing any one of claims 2-10.

23. A transmission and reception point, TRP (150), the TRP being adapted to:

send to a UE a first timing-advance value, TAV, for adjusting a first UE-stored TAV associated with a first UL BPL; and

send to the UE a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL, wherein

the second UE-stored TAV is distinct from the first UE-stored TAV, and

the second UL BPL is distinct from the first UL BPL.

24. A transmission and reception point, TRP (150), the TRP comprising:

a TAV-sending module (802) for sending to a UE: 1) a first timing-advance value, TAV, for adjusting a first UE-stored TAV associated with a first UL BPL and 2) a second TAV for adjusting a second UE-stored TAV associated with a second UL BPL, wherein

the second UE-stored TAV is distinct from the first UE-stored TAV, and

the second UL BPL is distinct from the first UL BPL.

25. A transmission and reception point, TRP (150), the TRP being adapted to: determine a first timing-advance value, TAV1, associated with a first UL BPL established with a UE;

determine a second timing-advance value, TAV2, associated with a second UL BPL established with the UE;

determine ΔΤ, wherein ΔΤ is absolute value of, TAV1-TAV2;

compare ΔΤ with a threshold; and

perform one of:

26. A transmission and reception point, TRP (150), the TRP comprising:

a determining module (902) configured to: determine a first timing-advance value, TAV1, associated with a first UL BPL established with a UE; determine a second timing- advance value, TAV2, associated with a second UL BPL established with the UE; and determine ΔΤ, wherein ΔΤ is absolute value of, TAV1-TAV2;

a comparing module (904) configured to compare ΔΤ with a threshold;

a generating module (906) configured to generate the same determined timing-advance adjustment to the first UL BPL and the second UL BPL in response to determining that ΔΤ is less than the threshold, wherein the determined timing-advance adjustment is equal to the minimum of TAV1 and TAV2, and

a deactivating module (908) configured to deactivate one of the first UL BPL and the second UL BPL in response to determining that ΔΤ is greater than the threshold.

27. A computer program (543) comprising program code (544) to be executed by at least one processor (555) of a transmission and reception point, TRP (150), wherein execution of the program code by the at least one processor causes the TRP to perform a method according to any one of claims 11-18.

28. A computer program (643) comprising program code (644) to be executed by at least one processor (655) of a user equipment, UE (150), wherein execution of the program code by the at least one processor causes the UE to perform a method according to any one of claims 1- 10.

29. A computer program product (541, 641) comprising the computer program according to at least one of claims 27 and 28, and a computer-readable storage medium (542, 642) on which the computer program is stored.