Patent Application
20240163808
The present invention relates to cellular wireless communication systems, and more particularly to power management in an integrated access and backhaul network of a cellular wireless communication system.
With the advent of fifth generation (5G) New Radio (NR) and an ever-increasing demand for high data rates, an enormous increase in backhaul capacity requirement is envisioned. Besides, to fulfil the needs of faster speeds, lower latencies and always-on connectivity, requirements of small cell densification, dynamic switching ON and OFF of small cells, and mobile backhaul are foreseen. The above mentioned needs from a wireless network can be fulfilled using a wireless channel with huge bandwidth for backhaul link. Thus, an Integrated Access and Backhaul (IAB) network using self-backhauling is necessitated.
In an IAB network, same channel is used in BH and AC links. Therefore, resource multiplexing between the Parent BH link, Child BH link and Child AC link is a crucial task. Resource multiplexing may be done in one of time, frequency, and space domain, leading to one of a time division multiplexing (TDM), frequency division multiplexing (FDM) and Space division multiplexing (SDM) schemes, respectively. In FDM and SDM schemes, the BH and AC transmissions or BH and AC receptions exist simultaneously. IAB nodes with FDM and SDM capability with half duplex constraints can operate in either simultaneous transmission mode or simultaneous reception mode. In case of FDM, interference between downlink (DL) transmissions or receptions and uplink (UL) transmissions or receptions will occur due to adjacent channel leakage. In case of SDM, interference between DL transmissions or receptions and UL transmissions or receptions will occur due to inter beam interference. In a TDM scenario, the Reference IAB node transmits in the BH-UL (to its Parent IAB node) and AC-DL (to its Child IAB node or AC UE) in different time slots. The BH efficiency may be improved by increasing the UL transmission power of the MT of the Reference IAB node beyond the desired UL power set by conventional UL power control. The increment in the UL transmit power may be upto the maximum transmit power capability of the Reference IAB node. However, sudden increment of UL transmission power upto the maximum limit may cause interference in other ongoing transmission in a network. Thus, there is a need for power management for interference mitigation and improving BH efficiency in FDM, SDM and TDM.
Consider a multi-hop IAB network with a Reference IAB node, having a Parent IAB node and one of Child IAB nodes and AC UEs. In simultaneous reception scenario, the Reference IAB node receives in both the BH and one of Child BH and AC link simultaneously. Simply put, there is DL reception from the Parent IAB node and UL reception from one of the Child IAB node and AC UE. The UL transmission from the Child IAB node or AC UE is under power control by the DU of the Reference IAB node and hence, the UL power from the Child IAB node, received at the Reference IAB node may be less than the DL power received from the Parent IAB node causing power imbalance in simultaneous reception. Therefore, the DL power from the Parent IAB node creates interference to the UL reception from the Child IAB node at the DU of the Reference IAB node, both in FDM and SDM scenario. In SDM, if the beams are overlapping, it causes inter beam interference. Inter beam interference is especially more severe in IAB nodes with single panel. The basic method to avoid interference is to choose beams that are far apart, so that the effect of interference is negligible. However, due to limitations in analog beam forming and relative position of the Parent IAB node and one of the Child IAB node and AC UE, it may be desired to choose beams that are overlapping in certain situations. In such cases, the interference from DL will affect the UL reception. Therefore, power control for DL transmission from IAB node is crucial.
In a simultaneous transmission scenario, the Reference IAB node simultaneously transmits in both the BH-UL to the Parent IAB node and AC-DL to the Child IAB node. For IAB nodes with multiple panels, there are different radio frequency (RF) Chains for transmissions in BH and AC links, hence no power sharing is required between transmissions from different panels. However, power sharing is crucial for IAB nodes with single panel, as there is a constraint on the maximum power. Since a power amplifier is shared between the MT of the Reference IAB node and DU of the Reference IAB node, there is further a need for a balanced power sharing between the MT and the DU part of the Reference IAB node.
Thus, there remains a need to manage and control power in an IAB network to improve overall performance of the network.
A general objective of the present invention is to provide methods of power management including power control methods for interference mitigation and BH efficiency as well as power sharing in IAB network.
Another objective of the invention is to mitigate transmission power imbalance in simultaneous receptions.
Still another objective of the present invention is to split power between BH and AC links in a manner to ensure successful transmission in BH and AC links satisfying maximum power limit but also to mitigate transmission power imbalance in simultaneous transmissions, if any, by limiting the maximum power per link.
Yet another objective of the present invention is to reduce DL power to enable power saving at the IAB nodes, making the technology sustainable.
The present invention relates to a method of power management in an integrated access and backhaul link.
The present invention relates to a method of interference measurement for power management in an integrated access and backhaul (IAB) network. The method may comprise requesting by a Reference IAB node for configuration of a Downlink-Reference Signal (DL-RS) for measurement of interference. The request may be made to one of a Parent IAB node, by sending a trigger from a Mobile Termination (MT) of the Reference IAB node, and a Donor IAB node, by sending a request for instruction to the Parent IAB node for the configuration of the DL-RS, from a Distributed Unit (DU) of the Reference IAB node. The Parent IAB node may signal a configuration information of at least one of a periodic DL-RS, aperiodic DL-RS and semi-periodic DL-RS to one of the MT of the Reference IAB node and DU of the Reference IAB node. The MT of the Reference IAB node may share the configuration information of the DL-RS with the DU of the Reference IAB node, when the configuration information is provided to the MT of the Reference IAB by the Parent IAB node. The DU of the Reference IAB node may receive a signal at a location of the DL-RS on an Uplink (UL) reception beam. The DU of the Reference IAB node may measure interference in time-frequency resources where the DL-RS is scheduled.
In one aspect, the trigger may have a length of at least one bit.
In one aspect, the measurement of interference may include at least one of a Reference Signal Receive Power (RSRP), Received Signal Strength Indicator (RSSI), and Reference Signal Received Quality (RSRQ).
In one aspect, the configuration information of the DL-RS may include at least one of a time location of RS and frequency location of RS, RS sequence, RS precoder, and RS transmit power.
In one aspect, no transmission in the UL may be scheduled by the Reference IAB node for the Child IAB node in the time-frequency resources where DL-RS is scheduled, to enable accurate measurement of the interference.
In another aspect, one of a Mobile Termination (MT) of a Reference IAB node and a Distributed Unit (DU) of the Reference IAB node may request a Parent IAB node, for configuration of a Downlink (DL) signal and a DL signal transmission power, for measurement of pathloss, and a Donor IAB node, for instructing a Parent IAB node for configuration of a DL signal and a DL signal transmission power for measurement of pathloss. The Parent IAB node may signal a configuration information of the DL signal for the measurement of pathloss. The Reference IAB node may receive the configuration information of the DL signal. The Reference IAB node may estimate a pathloss between a DL transmission beam of the DU of the Parent IAB node and an Uplink (UL) reception beam of the DU of the Reference IAB node, based on DL signal transmit power information available at the Reference IAB node. The Reference IAB node may measure a gain of the UL reception beam at the DU of the Reference IAB node in the direction of a Downlink (DL) beam of the Parent IAB node. The Reference IAB node may determine a threshold value of receiver gain of UL reception beam based on at least one of a maximum tolerable interference power, measured pathloss, and DL transmission power from the Parent IAB node. A comparison of a value of measured gain with a threshold gain of UL reception beam may be utilized for determining level of interference caused by DL reception from the Parent IAB node on the UL reception from the Child IAB node.
In one aspect, the DL signal may be one of a Downlink Reference Signal (DL-RS), Synchronization Signal Block (SSB), DL data channel, or control channel.
In one aspect, the configuration information may include at least one of a time locations, frequency locations, RS sequence, RS transmit power, channel content and channel average power.
In one aspect, estimation of pathloss may be done by one of the MT of the Reference IAB node for intra panel scenario and the DU of the Reference IAB node for inter panel scenario.
In one aspect, the direction of the DL beam of the Parent IAB node may be provided by the MT of the Reference IAB node to the DU of the Reference IAB node.
In one aspect, the maximum tolerable interference power at the DU of the Reference IAB node may be derived using UL target received power of the access link.
In one aspect, the value of measured gain greater than the threshold gain of the UL reception beam may indicate significant interference in the UL reception beam and the value of measured gain less than the threshold gain of the UL reception beam may indicate negligible interference in the UL reception beam.
In another aspect, a Reference IAB node may send a power ratios authentication request in one of Uplink Control Information (UCI) and Uplink (UL) data, to a Parent IAB node. The Parent IAB node may signal at least one of start time of simultaneous operation in Backhaul (BH) link in Downlink (DL) and Access (AC) link in UL of the Reference IAB node, by one of a Donor node and a Mobile Termination (MT) of the Reference IAB node, and a number of symbols (N) present between a symbol where authentication request is sent and a first symbol of simultaneous operation by the Reference IAB node. The Parent IAB node may determine if there is a change in power of at least one of a first Downlink (DL) signal, a first DL channel, and associated power ratios at a Distributed Unit (DU) of the Parent IAB node which causes a corresponding change in power of one of current and upcoming channels linked to at least one of the first DL signal and the first DL channel. The Parent IAB node may perform one of sending an authentication indicator to the MT of the Reference IAB node, if the same power ratios will be used for the DL transmissions at DU of the Parent IAB node, and informing value of new power ratios to the MT of the Reference IAB node, if there is a change in the power ratios of DL transmissions at DU of the Parent IAB node. The Reference IAB node may measure interference caused by BH-DL reception of at least one of the DL signal, and the DL channel at AC-UL reception using power ratios and at least one of power of Channel State Information Reference Signal (CSI-RS) and power of Synchronization Signal Block (SSB) configured to the MT of the Reference IAB node.
In one aspect, the power ratios may include ratio of power of at least one of DL data, DL control, DL signal, and channel power to one of the CSI-RS and the SSB.
In one aspect, the new power ratios may be shared through at least one of Radio Resource Control (RRC), Medium Access Control-Control Element (MAC-CE), and Downlink Control Information (DCI).
In one aspect, the value of the number of symbols (N) may range between a maximum and a minimum value. The maximum value may be a duration between the last symbol of downlink control information transmitted at a DU of the Reference IAB node for scheduling UL transmission at the MT of the Child IAB node and the start time of simultaneous operation at the Reference IAB node. The minimum value may be processing time required by the Reference IAB node for the simultaneous operation.
In one aspect, the processing time required by the Reference IAB node may be based on at least one of MT Physical Downlink Control Channel (PDCCH) decoding, Physical Data Shared Channel (PDSCH) reception preparation time, and DU scheduling time for the Child IAB node.
In another aspect, a Reference IAB node may measure an interference power using at least one of a Downlink Reference Signal (DL-RS), Synchronization Signal Block (SSB), Downlink (DL) data channel, and control channel, from Parent IAB node. The Reference IAB node may report an assistant information of resources where interference occurred, to one of the Parent IAB node and a Donor node. The Parent IAB node may perform DL power control in the reported resources.
In one aspect, when the interference is measured, the Reference IAB node may calculate a Signal to Interference and Noise Ratio (SINR) and may derive a corresponding value of at least one of Channel Quality Indicator (CQI) and Modulation and Coding Scheme (MCS).
In one aspect, the assistant information of resources may be reported when at least one of a calculated value of the CQI is less than a target CQI value and the interference from a DL beam from the Parent IAB node is significant at Reference IAB node.
In one aspect, the DL power control may be performed by a Distributed Unit (DU) of the Reference IAB node. The DU of the Reference IAB node may inform an interference power to the Mobile Termination (MT) of the Reference IAB node. The MT of the Reference IAB node may signal an indication of increase in the interference to the Parent IAB node. The DU of the Reference IAB node may also inform an indication of increase in interference, to the Donor IAB node. The Donor IAB node may request to configure DL power reduction at the Parent IAB node.
In one aspect, the Parent IAB node may receive a signal for the DL power control, from any one of the MT of the Reference IAB node, by including an additional indication of increase in interference in UL, the Donor IAB node, and the DU of the Reference IAB node, through at least one of a new signal and channel.
In one aspect, the Parent IAB node may check for a change in beam pair. The Parent IAB node may perform one of a modification in DL power based on the increase in interference when there is no change in beam pair, and calculation of new DL power for a newly latched beam pair, when there is a change in beam pair. The Parent IAB node may indicate newly latched beam pair index to the Reference IAB node through at least one of a Downlink Control Information (DCI) and Medium Access Control-Control Element (MAC-CE) signalling.
In one aspect, the signalling may be performed using at least one of physical layer signalling, MAC-CE signalling, and RRC signalling.
In another aspect, a Parent IAB node may configure a Reference IAB node with Downlink Reference Signal (DL-RS) for interference measurement and to feedback value of Downlink (DL) channel quality. The Parent IAB node may receive at least one of an indication of interference and the value of DL channel quality. The Parent IAB node may compare the value of DL channel quality with a target DL channel quality value. The Parent IAB node may assess fulfilment of the request for DL power reduction, wherein if the reported DL channel quality is lower than the target DL channel quality value, the request for DL power reduction cannot be fulfilled and the Reference IAB node switches to Time Domain Multiplexing (TDM) mode. When the reported DL channel quality is higher than the target DL channel quality, the Parent IAB node may perform one of reduction of the DL power for a time duration, performing link adaptations techniques for reduction of DL power, and indicating, by the Parent IAB node, a command for adjustment of received beam gain of the Uplink (UL) reception beam in a direction of the Parent IAB node to the Reference IAB node.
In one aspect, the assessment of fulfilment of the request for DL power reduction may include assessment of a target Downlink Modulation and Coding Scheme (DL-MCS) being not affected by the reduction in DL power and a power of at least one of Synchronization Signal Block (SSB) and Channel State Information Reference Signal (CSI-RS) not being compromised.
In one aspect, the link adaptation techniques may include at least one of reducing Modulation and Coding Scheme (MCS), and reducing number of spatial layers.
In one aspect, the Parent IAB node may indicate an adapted change for reduction of the DL power for the time duration to the Reference IAB node through one of downlink control information (DCI) and MAC-CE signalling.
In one aspect, the Parent IAB node may monitor for expiration of a timer associated with an allotted time duration with reduced DL power, and upon expiry of the timer and using at least one of a conventional DL power defined for New Radio (NR) systems, and a last updated DL power, based on an indication received from the Reference IAB node within the timer duration to use the last modified DL power.
In one aspect, the Parent IAB node may wait for a next DL power reduction request until expiry of the timer, and using modified DL power after assessment of the request for a further DL power reduction.
In another aspect, a Reference IAB node may detect interference caused by the Downlink (DL) reception from a Parent IAB node on Uplink (UL) reception from at least one of a Child IAB node and an access link in any one of Frequency Division Multiplexing (FDM) and Space Division Multiplexing (SDM) modes. The Reference IAB node may send a request for reduction in DL power by an offset to the Parent IAB node. The Parent IAB node may decrease, the DL power based on the request for DL power reduction. The Parent IAB node may acknowledge by indicating the reduction in DL power to the Reference IAB node for the request for reduction in DL power.
In one aspect, the request for reduction in DL power may be in the form of a TPC request. The TPC request may be one of existing format of TPC offset values described in New Radio (NR) for UL, one bit indication, a new offset value and a range of TPC values with a number of levels.
In one aspect, the Parent IAB node may determine a range of negative TPC values starting from zero to a negative minimum value depending on a target MCS and minimum transmit power of the DU of the Parent IAB node with a defined step size.
In one aspect, the decrement in DL power by the Parent IAB node may be in form of a defined step size within the range of negative TPC values and may be decreased until a last value of TPC in the range is reached.
In one aspect, the Parent IAB node may monitor a timer for expiration of a time duration after receiving the TPC request for the decrement in DL power.
In one aspect, the Parent IAB node may use one of a conventional DL power as defined for New Radio (NR) systems, and a modified DL power based on the received TPC request, when an indication from the Reference IAB node to use the modified DL power may be received within the timer duration, when the timer expires.
In one aspect, the Parent IAB node may wait for next TPC request, until expiry of the timer.
In one aspect, the request for DL power reduction may be sent using at least one of User Control Information (UCI) signalling, Medium Access Control (MAC) signalling, and along with Uplink (UL) data.
In another aspect, a Reference IAB node may detect an interference occurring in resources used for Uplink (UL) reception in access link by adjacent resources used for the BH-DL reception when the Reference IAB node uses Frequency Division Multiplexing (FDM) for the reception. The Parent IAB node may receive one of a request for reduction in DL power and associated resources from the Reference IAB node and instruction by the Donor IAB node for the reduction in DL power and associated resources. The Parent IAB node may reduce a DL transmission power to the received resources.
In one aspect, the resources for the request of reduction in DL power may be edge Resource Blocks (RBs) of bandwidth part allocated to an MT of the Reference IAB node, wherein with the reduction in DL power by the Parent IAB node, the interference at adjacent Uplink (UL) reception at DU of Reference IAB node is minimized and the edge RBs are utilized.
In one aspect, the MT of the Reference IAB node may send the request for reduction in power of associated resources by including one bit signal in any of an Uplink control information (UCI) and Medium Access Control (MAC).
In one aspect, the Parent IAB node may reduce the DL transmission power for the edge RBs by using at least one of transmitting power equal to half of power in center RBs, transmitting power equal to UL power of adjacent RBs used for reception from access link at the DU of the Reference IAB node, transmitting less power consuming signals in the edge RBs, power control in the edge RBs utilizing a decrement in power offset received from the Reference IAB node in User Control Information (UCI) and minimum power required for at least one of Synchronisation Signal Block (SSB) and Channel Status Information Reference Signal (CSI-RS).
In another aspect, a Parent IAB node may determine an initial minimum Downlink (DL) target power. The Parent IAB node may configure and trigger the resources for measurement and feedback of information of pathloss and a link quality. The Reference IAB node may report a parameter indicating a Downlink Pathloss and the link quality measurement, to the Parent IAB node. The Parent IAB node may determine a DL transmission power of the link to the Reference IAB node based on at least one of the parameter indicating the Downlink Pathloss, the link quality measurement, and minimum Downlink (DL) target power.
In one aspect, the initial minimum Downlink (DL) target power may be equal to an uplink (UL) target power scaled with an offset, wherein the offset may be dependent on at least modulation and coding scheme (MCS) used by the Parent IAB node.
In one aspect, the DL transmission power of the link to the Reference IAB node may be determined by adding at least one of a value of the Downlink Pathloss and an offset determined by the Parent IAB node based on the received link quality measurement report to the minimum DL target power.
In one aspect, the parameter may indicate the Downlink Pathloss and link quality measurement signalling may be reported using at least one of physical layer signalling, Medium Access Control-Control Element (MAC-CE) signalling, and Radio Resource Control (RRC) signalling.
In another aspect, a Reference IAB node may transmit an indication of requirement of increase in Backhaul Uplink (BH-UL) power beyond desired UL power decided by UL power control parameters, to a Parent IAB node. The Parent IAB node may send Transmit Power Control (TPC) commands with increased step size for the BH-UL from the Reference IAB node to reduce the number of TPC signalling for increase in UL transmit power. The Parent IAB node may signal an initial threshold UL transmit power to the Reference IAB node. The Reference IAB node may monitor receipt of the TPC command. The Reference IAB node may increase the UL transmit power with the defined step size upon receiving every TPC command, when the UL transmit power is less than the threshold UL power.
In one aspect, the Reference IAB node may transmit with power equal to previous UL transmission power to the parent IAB node, when no TPC command is received.
In one aspect, the Reference IAB node may compare the UL transmit power with the threshold UL power when the TPC command is received, and may stop the increase of UL power when the UL transmit power is more than or equal to the threshold UL power.
In one aspect, the signalling between Parent IAB node and Reference IAB node may be performed using at least one of Radio Resource Control (RRC) signalling, Medium Access Control-Control Element (MAC-CE) signalling, and physical layer signalling.
In one aspect, the initial value for the threshold UL transmit power may be determined using at least one of channel condition of network, and DL power spectral density.
In one aspect, the threshold UL transmit power may be less than or equal to maximum available power at the Reference IAB node.
In one aspect, the Parent IAB node may receive an information of interference caused to other ongoing transmission by the increased UL transmit power of Reference IAB node from at least one of a Donor node and a victim IAB node. The information of interference may be received by the Donor IAB node from the victim IAB node. The Parent IAB node may reassign a new value for the threshold power equal to the UL transmit power at the instant of interference based on information from at least one of the Donor IAB node and the victim IAB node.
In another aspect, a Reference IAB node may detect power constraint when the Reference IAB node is using single panel for transmitting uplink (UL) and downlink (DL) traffic in both backhaul link and access link in any of Space Division Multiplexing (SDM) mode and Frequency Division Multiplexing (FDM) mode. An MT of the Reference IAB node may allot an Uplink (UL) transmit power based on a UL power control indication from a Parent IAB node. The Reference IAB node may receive an indication of required DL transmit power using a UL control channel from a Child IAB node. The Reference IAB node may compute a DL transmit power based on at least one of the indication of required DL transmit power, the target throughput, Bit Error Rate, total remaining available power, and a parameter for Pathloss to the Child IAB node. The Reference IAB node may compute the DL transmit power to the access link. The Reference IAB node may allot a remaining power to one of backhaul link to the Parent IAB node and one of access link to the user and backhaul link to the Child IAB node, based on load.
In one aspect, the indication for required DL transmit power may be one of an absolute power value, and is present as increments or decrements in existing power values.
In one aspect, the parameter for Pathloss to the Child IAB node may indicate DL Pathloss of backhaul link to the Child IAB node. The DL Pathloss may be considered as equal to UL Pathloss of the link measured by the Reference IAB node, based on reciprocity.
In one aspect, the Reference IAB node may compute the DL transmit power to the access links to users based on at least one of achievement of five percentile performance at required distance at a cell edge, power requirement of cell specific signals including at least one of Synchronization Signal Block (SSB), Channel State Information Reference Signal (CSI-RS), and the power available after allocation of UL transmit power to Parent IAB node and DL transmit power to Child IAB node.
In one aspect, the Reference IAB node may share total available power for DL access link equally among various DL channels in the access link.
The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those of ordinary skill in the art. Moreover, all statements herein reciting embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
The present invention relates to methods of power management in an Integrated Access and Backhaul (IAB) network. The present invention discloses methods of measuring and reporting interference in simultaneous reception in at least one of FDM and SDM modes and interference in TDM modes in an IAB. The present invention further discloses power control processes for mitigation of interference. One or more combination of the described methods may be used to mitigate interference using power control.
In one embodiment, interference may be measured based on interference emulation using Reference Signals (RS). Consider a Reference IAB node may be simultaneously receiving data from its Parent IAB node and the Child IAB node in Space Division Multiplexing (SDM) mode with overlapped time-frequency resources. The Reference IAB node may be experiencing packet failure in transmission and reception of uplink (UL) and downlink (DL) traffic in both backhaul link and access link. If IAB node finds that there are many packet failures, the Reference IAB node initiates measurement of interference and indicates to the Parent IAB node. The interference caused by the DL reception may be measured at the Distributed Unit (DU) of the Reference IAB node. The interference may be measured using Reference Signals (RS). In 4th generation (4G) and 5th generation (5G) wireless communication systems, the RS includes various DL Reference Signals (DL-RS) such as Channel State Information-Reference Signals (CSI-RS), Demodulation Reference Signal (DMRS), and Phase Tracking Reference Signal (PTRS) on which the interference can be measured. Besides the existing reference signals, a new reference signal may also be used for the purpose of the interference measurement. A request for configuration of the DL-RS for interference measurement is sent by the Reference IAB node. A Mobile Termination (MT) of the Reference IAB node may send a request to the Parent IAB node to configure the DL-RS. This is achieved using a trigger sent in control information part of channel from MT of the Reference IAB node to the Parent IAB node. A request may also be sent by the DU of the Reference IAB node to the Donor IAB node for configuration of the Parent IAB node for DL-RS transmission periodically, semi periodically or in an aperiodic way. The Parent IAB node may configure the DL-RS for transmission either on a periodic, semi-periodic basis or aperiodic basis. The allocated DL-RS configuration information containing time-frequency locations of RS, RS sequence, RS precoder and RS transmit power, may be signalled by the DU of the Parent IAB node to one of the MT of the Reference IAB node or the DU of the Reference node. The allocated DL-RS configuration information may also be shared with the DU of the Reference IAB node by the Donor IAB node by getting configuration information from the Parent IAB node, if the RS request went to the Parent IAB node through the Donor IAB node. The configuration information of the DL-RS may also be shared by the MT of the Reference IAB node with the DU of the Reference IAB node, when the configuration information is provided to the MT of the Reference IAB by the Parent IAB node.
Measurement of interference may be performed by the DU of the Reference IAB node in the UL resources in which the corresponding DL-RS are present. The Reference IAB node may not schedule any transmission in the UL for the Child IAB node, in order to enable accurate interference measurement in the corresponding time-frequency resources where the DL-RS are scheduled. Since, no transmission is scheduled by the Reference IAB node for the Child IAB node, the received signal at the DL-RS resource locations contains only the interference signal and the noise. The measurement of interference may be in terms of at least one of Reference Signal Receive Power (RSRP), Received Signal Strength Indicator (RSSI), and Reference Signal Received Quality (RSRQ).
In one embodiment, interference may be measured proactively before actual Uplink (UL) reception, using UL reception beam.
PLcalculated=PLactual−Gr−Gt,
In the above mentioned equation, PLactual denotes the coupling gain created by a channel in dB, Gt denotes an antenna gain at the transmitter in dB and Gr denotes an antennae gain at the receiver in dB.
PLcalculated+A(θ)=PLactual−Gt,
In the above mentioned equation, the parameters PLcalculated and A(θ) are known.
For a target Channel Quality Indicator (CQI) or a Modulation and Coding Scheme (MCS) required in the UL reception from the Child IAB node to the Reference IAB node, the minimum required Signal to Interference and Noise Ratio (SINR) may be computed. The maximum tolerable interference power Pint, max may be derived from the minimum SINR required and target received power PO. Interference seen at Reference IAB node is the unwanted reception at DU due to DL transmit power Pt from the Parent IAB node may be given as the following equation:
Pint=Pt−(PLactual−Gt−Gr),
In the above mentioned equation, using the computed values of (PLactual−Gt) from the second equation and taking DL transmit power Pt as constant, threshold Pint,max will provide threshold value of receiver gain Gr at the DU of the Reference IAB node, i.e., Gr0. The value of Pt is either considered to be equal to any known DL-RS transmission power or obtained from the Parent IAB node as an average DL power. If A(θ) is greater than or equal to Gr0, it means there is high interference from DL transmission at the DU. Thus, one of a modification in receiver gain at the DU and change in DL transmission power of Parent IAB node is needed.
In one embodiment, the interference may be measured using power ratios configured by the Parent IAB node. Considering a New Radio system, the Base Station (BS/gNB) sends DL power offsets for various DL signals and channels. These offsets are considered as power ratios by UEs. The UE considers that the power of all DL signals or channels are associated with each other in such a way that any change in the power of a particular signal will change the power of the signal(s) or channel(s) linked with it by the associated power ratios. For simultaneous reception of IAB BH and AC links, the Reference IAB node may use the power ratios and one of a CSI-RS (Channel State Information-Reference Signal) or Synchronization Signal Block (SSB) power configured to the MT of the IAB by the Parent IAB node to predict the approximate power of all DL signals or channels transmission including data transmission at or before start of or during the simultaneous operation. The predicted power may be used to measure the upcoming or ongoing interference caused by BH-DL reception at AC-UL reception in a proactive way. The power ratios may include ratio of power of at least one of DL data, DL control, DL signal, and channel power to one of the CSI-RS power and SSB power.
The power ratios may also be used along with previous methods for interference measurements performed using RSs to get more accurate value of interference caused by DL data channels. Last DL PL or RSRP measured by the MT of the Reference IAB node may be used for the interference prediction of any particular channel or signal including data as given by following equation:
P
data
=R
1
*P
CSI-RS,
In the above mentioned equation, Pdata denotes DL data channel transmission power and PCSI-RS denotes CSI-RS transmit power.
Thus, the above equation may be written as below equation,
Intdata(dB)=Pdata(dB)−PL(dB) (or) Intdata(Linear)=R1*RSRPCSI-RS
In the above mentioned equation, R1 denotes linear value of power offset or ratio of DL data power to CSI-RS power, Intdata denotes Interference caused by DL data received at Reference IAB, and RSRPCSI-RS denotes linear value of RSRP measured at CSI-RS.
The Reference IAB node may send an authentication request to the Parent IAB node for the power ratios either in UCI or along with UL data. The Parent IAB node may respond with the authentication indicator in at least one of radio resource control (RRC), medium access control-control element (MAC-CE) or downlink control information (DCI) if the same power ratios will be used for the upcoming DL transmissions at the DU of the Parent IAB node. Upon change in DL transmission power, the associated new power ratio values may be informed to the MT of the Reference IAB node by the Parent IAB node through one of the RRC, MAC-CE or DCI. If the power changes after the start of simultaneous reception, then the new ratios may be informed again dynamically. It may be beneficial for the Parent IAB node to know the start time of simultaneous operation of the Reference IAB to send the authentication or the values of ratios. The start time may be either informed by the Donor IAB node or the MT of the Reference IAB node in UL of the Reference IAB node before starting the simultaneous operation to the Parent IAB node.
In another embodiment, the Reference IAB node may send an authentication request to the Parent IAB node for the power ratios either in UCI or along with UL data. The authentication request may also serve the purpose of start time indication for simultaneous reception and is sent at N symbols or slots before first symbol of simultaneous reception. The value of number of symbols (N) is informed to the Parent IAB node by the Reference IAB node. Here, first symbol of N symbols is between the last symbol of DCI scheduling UL transmission at Child IAB node and the minimum processing time required by the Reference IAB node for the simultaneous operation. The Reference IAB node determines the number of symbols or slots (N) between the symbol or slot where authentication request is sent and the first symbol or slot of simultaneous operation considering Physical Downlink Control Channel (PDCCH) decoding, Physical Data Shared Channel (PDSCH) reception preparation time and DU scheduling time for Child IAB node.
In one embodiment, the measured value of interference may be reported. The resulting SINR is calculated based on a calculated interference power at the Reference IAB node and the corresponding value of CQI or MCS may be found out. The interference power is calculated using at least one of a Downlink Reference Signal (DL-RS), Synchronization Signal Block (SSB), DL data channel, and control channel, from Parent IAB node. If the calculated value of CQI or MCS is less than the target value and the interference due to DL reception is also significant at the Reference IAB node, then the Reference IAB node will convey information of the interference and the resources where interference occurred to the Parent IAB node. The information may be shared from DU of the Reference IAB node to the MT of the Reference IAB node. The MT of the Reference IAB node may inform the Parent IAB node by at least one of Li control signaling, MAC-CE or through other higher layer parameters. In 4G and 5G systems, the control channel signalling is termed as UL control information (UCI). Additional field for indication of increase in interference may be included in at least one of UCI, MAC-CE or Higher layer signalling.
The resources where the interference occurred may also be reported to the Parent IAB node as an assistant information, such that the Parent IAB node may perform selective DL power control specifically to the resources reported by the Reference IAB node and may use conventional DL power allocation for the remaining resources. Alternately, the DU of the Reference IAB node may also inform this to the Parent IAB node through the Donor IAB node or any new channel may also be used for this signalling from Reference IAB node to the Parent IAB node as an indication for interference requesting DL power reduction. The Parent IAB node may consider the request for modification in DL power until the same beam pair is latched and after the beam pair changes, Parent IAB node will stop using the DL power modified by the request received for previous latched beam pair and calculates new DL power for the new beam pair. The newly latched beam pair index is indicated by the Parent IAB node to the Reference IAB.
In one embodiment, power control procedures may be used to mitigate interference. The DL transmit power may be decreased using at least one of link adaptation techniques and adjusting beam gain. The Parent IAB node, upon receiving the indication from the Reference IAB node, will consider decreasing the DL transmit power or decide to use other link adaptations techniques to decrease DL power. The other link adaptations techniques include using lower order MCS, reducing number of layers transmitted to decrease DL power. The decreased DL transmit power will be applied up to a certain time period such as up to a timer expiry and is signalled to the Reference IAB node. The Parent IAB node will use either the conventional DL power as in NR or last updated DL power after the timer expires based on a signal received from the Reference IAB node until a new indication for DL power is received by the Parent IAB node. If a new indication comes within the timer duration, the Parent IAB node will consider that also if it can afford further reduction in DL power. However, the reduction in DL power is based on at least one of following constraints: (i) the power of important signals such as SSB and CSI-RS is not compromised (ii) the target DL MCS is not affected by the reduction in DL power. The parent IAB node configures its Child IAB node with DL reference signals for interference measurement and also configures the Child IAB node to feedback the DL channel quality values. The Parent IAB node will receive an indication for the interference and the value of DL channel quality from the Child IAB node. If the reported DL CQI from the childIAB node is higher than the target CQI, the parent IAB node will decrease its DL transmission power.
If the above constraints are not satisfied, the DL power cannot be reduced, and then the Reference IAB node will switch to TDM mode. Alternatively, adjusting the value of Gr (receive beam gain) of the UL reception beam, in the direction of the Parent IAB node will be done to mitigate power imbalance issue.
In one embodiment, partial power control in DL based on Transmit Power Control (TPC) command may be used to mitigate interference. Considering a Reference IAB node operating in simultaneous reception from BH-DL and either BH-UL or AC-UL in either SDM or FDM mode, the issue of power imbalance arising may be solved by employing DL power control taking inspiration from existing UL power control. However, to adopt exactly same algorithm as used for UL in DL can be resource consuming and unnecessary increase network overhead. Thus, a practical way to mitigate the power imbalance issue causing interference in weaker signal is to use partial power control in DL. The Reference IAB upon facing interference at AC-UL reception by BH-DL reception may send negative TPC request to the Parent IAB node. Either the format of the TPC commands similar to those used in NR systems may be reused as TPC request or a one bit indication in UL may be used. The corresponding TPC values may be either the existing values described in NR or any other new values in the form of range with a number of levels. A range of negative TPC values may be determined by the Parent IAB node starting from zero to a negative minimum value depending on target MCS and minimum transmit power of the DU of the Parent IAB node. Upon receiving the TPC request, Parent IAB node may take into consideration for defining DL power, if it can afford the decrement in DL power. The Parent IAB node decreases the DL power with the defined step size with every TPC request until it reaches the last value of TPC in the range and gives acknowledgement to the Reference IAB node for the received TPC request. Parent IAB node may wait for next TPC request until a timer duration. After timer duration expires, Parent IAB node may stop the power control for DL and continue the transmission either with conventional DL power as defined for NR or with modified DL power based on the received TPC request, if the Reference IAB node sends an indication to use modified DL power within the timer. These TPC requests can be sent either in UCI, MAC or can be sent along with UL data. This method does not require exchange of all the parameters between Parent IAB node and Child IAB node, but takes into account only TPC part of power control making it a partial power control, which will help in DL transmit power reduction at parent IAB node side, thus reducing interference at Reference IAB node.
In one embodiment, the DL power is reduced in Edge resource blocks (RBs) for simultaneous reception using FDM. Considering a case of simultaneous reception from Parent IAB node and Child IAB node using FDM, the interference from the Parent IAB node can be avoided using guard band between the resources allocated for Parent IAB node and Child IAB node. However, due to high power difference in DL and UL receptions, there may still be interference.
In one embodiment, the DL power control is based on PL feedback and link quality without fractional PL compensation. Considering the DL power control, the DL transmission power is fixed based on the link quality and DL PL reported by the Reference IAB node. An initial minimum target power value is considered. The minimum target power is equal to the uplink target power used for the same link used by the Parent IAB node scaled with a first offset to account for the corresponding MCS used in DL. The first offset is dependent on modulation and coding scheme (MCS) used by the Parent IAB node. Thereby signaling of target DL power parameter from Reference IAB node is avoided. The Parent IAB node may configure and trigger the resources for measurement and feedback of pathloss and a link quality. The DL PL of the link and the link quality calculated by Reference IAB node may be reported to the Parent IAB node in one of the UCI, MAC, and RRC layer. The received DL PL value along with a second offset dependent on the link quality is added to the minimum DL target power by the Parent IAB node. The DL transmission power of the link is determined by the Parent IAB node based on the following equation:
DL power=DL target power+PL reported by reference IAB+second offset,
In the above mentioned equation, the DL target power denotes the target UL receive power scaled with DL MCS dependent offset. Full DL PL compensation is performed at the Parent IAB node for the PL reported by the Reference IAB node, thereby avoiding signaling of fractional PL compensation factor as used in UL power control. The value of second offset may either be additive or subtractive based on the channel quality. For example, for RBs with good channel quality this value may be negative. The only signalling needed here are DL pathloss and link quality measurement. Thus, a practical DL power control helps to resolve received power imbalance issue at Reference IAB node with less amount signalling.
In one embodiment, power control may be used for increasing BH efficiency by using TPC in case of TDM mode of resource multiplexing between Parent BH link and either Child BH link or Child AC links. For improved BH efficiency, the BH UL power may be increased compared to the UL power calculated based on UL power control, up to some limit. However, this is possible only in case of TDM based resource multiplexing between the Parent BH link and either Child BH link or Child AC link, since there is no scope of interference between BH and AC links in case of TDM scenario. The increase in UL transmit power may be done in steps using TPC commands up to the threshold indicated by the Parent IAB node. The Parent IAB node may decide the threshold based on channel condition of network, DL power spectral density and may be indicated by at least one of physical layer, MAC CE and RRC to the Reference IAB node. The step size for values of TPC command for an IAB node in TDM mode may be increased as compared to the existing values in NR. Table 1 illustrates TPC for increased efficiency in TDM multiplexing for BH and AC.
The method reduces the number of times the TPC command is transmitted for the same amount of increase in UL transmit power. The TPC command is transmitted by the Parent IAB node upon receiving indication of requirement of increase in BH-UL beyond desired UL power from Reference IAB node. At some point of time, the increased UL power may cause interference to other ongoing transmissions in the network. In such a case, the Victim IAB node experiencing interference due to the increased UL transmit power of Reference IAB node informs the Donor IAB node controlling the whole IAB network or Parent IAB node of the Reference IAB node. The Donor IAB node informs the Parent IAB node about the interference. The transmit power used at the instant where the interference occurs as informed by the Donor IAB node or victim IAB node can also be used as the new value for threshold power at the Parent IAB node. Then the Parent IAB node also take measures to reduce or stop increasing the UL transmit power of Reference IAB node.
In one embodiment, power control is used for power sharing between BH link and AC link in simultaneous transmission mode. Considering, the FDM and SDM scheme that enables simultaneous transmissions in both BH and AC links, proper power sharing methods between the BH and AC links is crucial for IAB nodes with single panel, as there is a constraint on maximum power. The power sharing mechanism considers the sharing of power between the UL and DL transmissions.
P
tot
=P
UL
+P
DL
In the above mentioned equation, Ptot denotes the total power shared between the UL and DL transmissions, PUL denotes the transmit power in UL BH, while PDL denotes the total power used for DL transmissions. The value of PUL is fixed based on UL power control, which is further determined based on target received power, pathloss, transmit MCS, number of allocated RBs etc. In case of DL transmissions, sharing of power between transmission to Child BH link and Child AC link may also be considered. The DL power sharing may be based on constraints pertaining to Child BH links and Child AC links. In case of Child BH link, the transmit power may be such that the required BH throughput is achieved, since the BH link is an essential link. The DL BH transmit power is decided based on either signaling from the Child IAB node to the Parent IAB node, using UL control channel, indicating the required transmit power or calculated at Reference IAB node. The signaling may be either absolute power value or the increments or decrements to the existing power value. In case of calculating power at Reference IAB node, the Reference IAB node computes the DL transmit power to the Child IAB node based on the target throughput. The required bit error rate (BER) is to be considered. For the target throughput of R and the required BER of Pe, the required data rate is R/(1−Pe). The MCS required to meet the above rate is found out. The pathloss measurements are performed in the UL and the same pathloss is considered in the DL, assuming reciprocity. Using UL pathloss value and required MCS, the DL transmit power may be calculated.
In case of AC UEs, the DL transmit power may be based on at least one of the following constraints: (i) At least 5 percentile performance requirement is achieved at the required distance (cell edge), (ii) the transmit power for important cell specific signals including SSBs and CSI-RS are as per the requirement.
Allocating equal power for Child BH and AC link to User Equipment (UE) may lead to decrease in the coverage of the Child BH link. For example, the coverage D1 is achieved if full power is used in BH, whereas the coverage reduces to D2 when the power is equally shared between UL-BH and DL-AC links. It is required that the coverage for Child BH is always greater than the maximum coverage for AC UE.
P
DL
=P
DL_BH
+P
DL_Acc
+P
EX,
In the above mentioned equation, PDL_BH denote the power transmitted over the Child BH link and PDL_Acc denote the power transmitted over the AC link to UEs. The factor PEX denotes the additional power remaining after power allocation to Child BH link, Parent BH link and AC link to UEs. Referring back to
In the above detailed description, reference is made to the accompanying drawings that form a part thereof, and illustrate the best mode presently contemplated for carrying out the invention. However, such description should not be considered as any limitation of scope of the present invention. The structure thus conceived in the present description is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202141011863 | Mar 2021 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN22/50252 | 3/16/2022 | WO |
