GB2577529A - Improvements in and relating to power control in integrated access and backhaul - Google Patents

Abstract

Disclosed is method of performing power control for transmission signals in a telecommunication system employing Integrated Access and Backhaul, IAB, comprising the steps of: determining whether Frequency, Time or Spatial Division Multiplexing, FDM, TDM, SDM is used on a particular pair of links; and applying a power control scheme accordingly. This addresses prior issues with IAB such as power imbalance or power splitting when signals are received or transmitted simultaneously on access and backhaul links.

Description

Improvements in and relating to power control in integrated access and backhaul The present invention relates to improvements in power control in Integrated Access and Backhaul (IAB) in a telecommunication network. IAB is used particularly in Fifth Generation (5G) or New Radio (NR) networks, but may be applicable in other systems also.

IAB is a technique whereby nodes may utilise radio links between themselves to provide backhaul connectivity, as well as radio links between nodes and User Equipment (UE) to provide access connectivity.

Figure 1 shows a prior art IAB setup showing three nodes A, B, C, where backhaul connectivity is provided via radio links between nodes A and B, and A and C respectively.

Node A is connected by fibre to the core network. Access radio links are also provided from nodes A and B to UE 10, from node B to UE 20, and from node C to UE 30.

In prior art IAB configurations, uplink power control is performed, but this does not address the problems encountered.

In practical IAB implementations, one of the problems encountered is power control for IAB nodes in Spatial Division Multiplexing (SDM)/Frequency Division Multiplexing (FDM). There are generally two issues as below: * Power imbalance when an IAB node receives simultaneously from its parent IAB node via backhaul (BH) link and from a UE via an access (AC) link. In such a case, the reception power from the parent IAB node is much higher than that from the UE and it can cause problems such as strong interference, ADC saturation, etc. * Power splitting when an IAB node transmits simultaneously to its parent IAB node via backhaul (BH) link and to a UE/child IAB nodes via access link. In such a case, the transmission power in the BH link is controlled by its parent node but the IAB node determines its own transmission power to the UE/child IAB nodes. These two power values are correlated and they may affect each other.

Embodiments of the present invention address these and other problems in the prior art.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent

claims, and the description which follows.

Embodiments of the invention address the power imbalance and power splitting problems associated with IAB nodes; they make the power control of IAB nodes more efficient.

According to an aspect of the present invention, there is provided a A method of performing power control for transmission signals in a telecommunication system employing Integrated Access and Backhaul, IAB, comprising the steps of: determining whether Frequency, Time or Spatial Division Multiplexing, FDM, TDM, SDM is used on a particular pair of links; and applying a power control scheme accordingly.

Preferably, the pair of links may be arranged according on one or more of the schemes: a parent IAB node/donor node link to a relay IAB node is TDMed with a UE link; a downlink parent IAB node/donor node link to a relay IAB node is FDMed with an uplink UE link; an uplink parent IAB node/donor node link to a relay IAB node is FDMed with a downlink UE link; a downlink parent IAB node/donor node link to a relay IAB node is SDMed with an uplink UE link and/or an uplink child IAB node to a relay IAB node; and an uplink parent IAB node/donor node link to a relay IAB node is SDMed with a downlink UE link and/or a downlink relay IAB node to a child IAB node.

Preferably, each of the schemes has associated with it at least one method of performing power control.

Preferably, power control steps applied to backhaul links, when compared to access links, are larger, greater in number or provided with a fixed step size with a step up/down indication.

Preferably, a message comprising information related to an interference level, such as RSRP or SINR, is transmitted from the relay IAB node to the parent IAB node, so that a transmission power of the parent IAB node may be adjusted.

Preferably, a transmission power of the UE can be adjusted by the relay IAB node by sending a power offset value via RRC, MAC CE or DCI.

Preferably, the relay IAB node splits available power between uplink backhaul links and downlink access links by means of one or more of power reservation; power compensation and power scaling.

Preferably, more than one of TDM, FDM and SDM are used simultaneously in a hybrid configuration.

Preferably, subframes associated with different multiplexing schemes are divided into multiple sets and different power control schemes are applied to different subframe sets either via explicit configuration or implicitly.

Preferably the different power control schemes are as identified in the following description prefaced with the labeld FDM, SDM or TDM, as appropriate.

Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which: Figure 1 shows a typical IAB configuration according to the prior art; Figure 2 shows an IAB configuration according to an embodiment of the present invention; and Figure 3 shows a flowchart showing a method according to an embodiment of the present invention.

Embodiments of the invention deal with different configurations of BH and AC link multiplexing schemes, namely Time Division Multiplexing (TDM), Frequency Division Multiplexing (FDM) and Spatial Division Multiplexing (SDM). The IAB system according to an embodiment is illustrated in Fig. 2. Illustrated are three network nodes including parent IAB node/Donor IAB node T1, relay IAB node T2 and child IAB node T3. For each IAB node, a UE is also associated with it -U1, U2, U3 respectively. The various links are illustrated and named according to the entities involved e.g. link T2U2 is the radio link between node T2 and UE U2.

The following description describes TDM, FDM and SDM configurations in turn. There are some commonalities, but some differences in approach for each case.

TDM

TDM is further divided into two cases: TDM1 -T1T2 is TDMed with T1 U1 In this case, the AC links are completely TDMed with BH links. In such a case, the AC link T1 U1 is TDMed with BH link T1T2. Normal power control procedure can be applied. However, considering the much larger transmission power range of an IAB node, the step size for closed-loop power control can be further enhanced. A lamer step size may be considered. This leads to the three following options which may be implemented, depending on the circumstances: * TDM1.1 Keep the power control command to 2 bits, meaning that four different update steps can be defined, e.g., {-3dB, OdB, 3dB, 5d13}.

Step size for T1 U1 Step size for T1 T2 -1 -3 0 0 1 3 3 5 * TDM1.2 Increase the number of bits for power control command to N bits where N>2.

For example, with 3 bits, 8 different update steps can be defined as {-5, -3, -1, 0, 1, 3, 5, 7}.

Step size for T1 U1 Step size for T1T2 -1 -5 0 -3 1 -1 3 0 - 3 * TDM1.3 A fixed step size [X] is used and step-up, step-down and no change can be indicated by two bits. One example can be '00' = no change, '01' = step-up, '11' = step-down.

Another embodiment involves the update rate of power control for BH links. Since BH links are far more steady (i.e. less likely to change so frequently) than AC links, the update rate can be made much lower to reduce the signaling overhead.

TDM2 -T1T2 can co-exist with T1 U1 In this case, the AC links can co-exist with BH links in the same hop. For example, the AC link T1U1 can co-exist with BH link T1T2. However, the AC links and BH links are separated in time, frequency or spatial domain via scheduling or by beam steering (MU-MIMO) and the same methods as described above in TDM1 can be applied as well.

FDM

FDM is further divided into two cases: FDM1 -Downlink (DL) T1 T2 + Uplink (UL) T2U2 In this case, parent IAB node T1 and UE U2 transmit to the IAB node T2 simultaneously in an FDM manner. There should be a guard band between BH band and AC band. However, since the transmission power of the IAB node can be much larger than the UE, any power leakage from the BH band to the AC band might cause interference to the AC links. In such a case, the following alternative implementations can be considered: * FDM1.1 Closed-loop DL power control: if the relay IAB node, T2, detects that the interference caused by the BH link to the AC link is too strong and that the performance of the AC link is significantly degraded, the relay IAB node, T2, can send a negative power offset value to its parent IAB node, Ti, to reduce the transmission power. Once the interference becomes acceptably low, the relay IAB node, T2, can either send a positive power offset to restore the transmission power of the parent IAB node, T1, gradually or send a power restore signal to restore the transmission power in one step. Such a message can be signaled via UCI in a dynamic manner.

* FDM1.2 Closed-loop DL power control: instead of sending a power offset, the relay IAB node, T2, can signal the interference situation to the parent IAB node, T1. Such an indication of interference can be the Signal to Interference plus Noise Ratio (SINR) of the access link, Reference Signal Received Power (RSRP) of the access link, ratio of RSRP of backhaul link and access link, etc. Such a message can be signaled via UCI in a dynamic manner.

* FDM1.3 Reset the UL power control: in order to prioritise the BH links, the parent IAB node, T1, transmission power is unchanged but UE UL transmission power control can add a power offset to the expected reception power. This offset can be signaled either semi-persistently via RRC, MAC or dynamically via DCI. However, it is possible that the UE cannot adjust its TX power, either because UE TX power has reached Pcmax or UE TX power has reached Pmin. In this case, this situation should be signaled to the parent IAB node, T1, so that the parent IAB node can decide if FDM1A, above, needs to be applied.

It should be noted that for FDM1.1, FDM1.2 and part of FDM1.3, the relay IAB node, T2, can only make recommendations, and the final decision is made by the parent IAB node, T1. Also, any recommendation can be overridden by the parent IAB node, T1.

FDM2 -UL T1T2 + DL T2U2 In this case, the transmission power of relay IAB node, T2, in UL T1T2 is controlled by its parent IAB node, T1, but the transmission power of relay IAB node, T2, in DL T2U2 is controlled by itself. The total transmission power should be split between the two links. Priority should be given to BH link T1T2 but for DL T2U2, some power needs to be reserved, e.g., power for reference signals such as SS and CSI-RS. In order to satisfy such requirements, the following alternatives can be implemented, as required: * FDM2.1 Reserved power for DL AC link is reflected in the UL BH power control. For example, the transmission power in UL BH link can be defined as min{Pcmax-reserved power, original power control equation}. This reserved power can either be pre-defined or signaled by the relay IAB node, T2, to the parent IAB node, T1, e.g., via UCI or MAC-CE (like PHR); * FDM2.2 Priority is given to BH links and it follows normal power control procedure.

For the AC links, if the power available for reference signals is not enough, the relay IAB node, T2, can signal the parent IAB node, T1, and, at the same time in the AC link, the data power can be temporarily borrowed to transmit reference signals.

* FDM2.3 Both the UL BH power control and AC link transmission power follow the normal procedure and if the final power summation is above the maximum transmission power of the relay IAB node, T2, these two power values can be scaled down to the maximum transmission power. Such power scaling should be signaled to the parent IAB node, T1, e.g., via UCI, so that it will not request higher transmission power for the IAB relay node.

* FDM2.4 Guaranteed maximum power can be defined for UL T1T2 and DL T2UE, respectively, namely P_UL for T1T2 and P_DL for T2UE. These values can be configured by parent relay node, T1, or the gNB. Basically, the relay node, T2, calculates transmission power for UL and DL. If the calculated power does not exceed the guaranteed power, then the relay node, T2, uses the calculated value. However, if the calculated power exceeds P_UL or P_DL, then it can be scaled. Here, there could be several different scenarios: o Scenario-1: the calculated power for UL (P1) > P_UL but the calculated power for DL (P2) < P_DL * Transmission power of UL can be scaled down and DL TX power is kept o Scenario-2: P1 < P_UL and P2 > P_DL * Transmission power of DL can be scaled down and UL TX power is kept.

o Scenario-3: P1 < P_UL and P2 < P_DL * No scaling o Scenario-4: P1 > P_UL and P2 > P_DL * Both need to be scaled * FDM2.5 Guaranteed minimum power can be defined for UL T1T2 and DL T2UE, respectively, namely P_UL for T1T2 and P_DL for T2UE. These values can be configured by the parent relay node or gNB. Basically, the relay node calculates transmission power for UL and DL. If the calculated power is not lower than the guaranteed power, then relay node uses the calculated power. However, if the calculated power is lower than P_UL or P_DL, power borrowing should be applied.

Here, there could be different scenarios: o Scenario-1: the calculated power for UL (P1) < P_UL but the calculated power for DL (P2) >= P_DL * Transmission power of DL can be borrowed to boost the UL Tx power o Scenario-2: P1 >= P_UL and P2 < P_DL * Transmission power of UL can be borrowed to boost DL TX power.

o Scenario-3: P1 >= P_UL and P2 >= P_DL * No scaling o Scenario-4: P1 < P_UL and P2 < P_DL * This scenario cannot happen

SDM

SDM is further divided into two cases: SDM1 -DL T1T2 + UL T2U2 Note that in the following, the terms inter-panel and intra-panel are used. In this context, inter-panel means multiple panels are available, each having its own RF chain and baseband processing capability. As such, each panel has its own power budget and power need not be shared between them. In the example of Figure 2, node T2 might be in communication with nodes T1 and T3 as well as UE U2. Each link has its own dedicated panel. In the intra-panel case, 1 panel is provided, having common RF chain and baseband processing, but serving several antennas/beams. In the example of Figure 2, the links from T2 to T1, T3 and U2 would all need to share power from a common power budget, even though they are sewed by separate beams/antennas.

* SMM1.1 (inter-panel) In such a case, concurrent reception with two separate basebands is assumed. The resources used by two links are overlapping and the IAB to UE interference problem could be more significant than FDM case. However, the same solutions identified in FDM above can be easily applied to SDM as well.

* SDM1.2 (intra-panel) In such a case, concurrent reception is via a single baseband is assumed. In addition to the interference problem aforementioned, another problem is that the received power from the DL T1T2 BH link could be much stronger than that from the UL T2U2 AC link. Under such circumstances, the operation of the Analog to Digital Convertor (ADC) could be a problem. If the conversion/quantization granularity of the received analog signal is based on the BH link power range, then for the AC link signal from UE U2 it could be too coarse. On the contrary, if the granularity conversion/quantization of the received analog signal is based on the AC link power range, then for the BEI link it could be unnecessarily fine. One solution is to use non-linear granularity where the granularity is finer for small power values and larger for large power values. Another option is to use coarse granularity for IAB signal first and once the IAB signal is detected, it can be removed from the received signal and then a finer granularity can be used for UE signal.

SDM2 -UL T1T2 + DL T2U2 * SDM2.1 (inter-panel) The transmission power splitting problem in FDM might also apply to SDM. However, for the inter-panel case with separate basebands, there may be two separate panels transmitting in UL T1T2 BH and DL T2U2 AC links and they do not need to share power. Without this power sharing constraint, each panel can configure its own transmission power and the power control in UL T1T2 BH link can also be separated from DL T2U2 AC link transmission power configuration. Therefore, a normal power control procedure can be followed.

* SDM2.2 (intra-panel) For the intra-panel case, power sharing between two links is needed. The same options described above as FDM2.1 -FDM2.5 can also be applied here.

In addition to the single multiplexing schemes described so far, it is also possible that a system supports a hybrid multiplexing scheme and different schemes/combinations are chosen depending on circumstances. As mentioned, different power control schemes may be applied for different multiplexing schemes and the configuration should either be implicitly or explicitly signaled. The following embodiments are provided: * Implicit: multiple subframe sets are defined for multiple multiplexing schemes and there is a pre-defined association between multiplexing scheme and power control algorithm applied. Once the sub-frame set type is known, the corresponding power control scheme can be chosen accordingly; * Explicit: the gNB explicitly indicates/configures which Closed Loop Power Control (CLPC) processes (i.e., the index T in power control formula) should be used for a certain slot format by DCI, MAC CE, RRC, etc. For the "explicit" case above, the configuration can either be centralized by the donor IAB node or distributed by each parent IAB node.

Figure 3 shows a flowchart illustrating the steps involved in signalling the step size for power control. This illustrates how the power control related configurations, according to embodiments of the present invention, for IAB, e.g., step size, are signalled from gNB to the UE or the other way around.

At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as 'component', 'module' or 'unit' used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of others.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (9)

1. CLAIMS1. A method of performing power control for transmission signals in a telecommunication system employing Integrated Access and Backhaul, IAB, comprising the steps of determining whether Frequency, Time or Spatial Division Multiplexing, FDM, TDM, SDM is used on a particular pair of links; and applying a power control scheme accordingly.
2. 2. The method of claim 1 wherein the pair of links may be arranged according on one or more of the schemes: a parent IAB node/donor node link to a relay IAB node is TDMed with a UE link; a downlink parent IAB node/donor node link to a relay IAB node is FDMed with an uplink UE link; an uplink parent IAB node/donor node link to a relay IAB node is FDMed with a downlink UE link; a downlink parent IAB node/donor node link to a relay IAB node is SDMed with an uplink UE link and/or an uplink child IAB node to a relay IAB node; and an uplink parent IAB node/donor node link to a relay IAB node is SDMed with a downlink UE link and/or a downlink relay IAB node to a child IAB node.
3. 3. The method of claim 2 wherein each of the schemes has associated with it at least one method of performing power control.
4. 4. The method of claim 2 or 3 power control steps applied to backhaul links, when compared to access links, are larger, greater in number or provided with a fixed step size with a step up/down indication.
5. 5. The method of any of claims to 4 wherein a message comprising information related to an interference level, such as RSRP or SINR, is transmitted from the relay IAB node to the parent IAB node, so that a transmission power of the parent IAB node may be adjusted.
6. 6. The method of any of claims 2 to 5 wherein a transmission power of the UE can be adjusted by the relay IAB node by sending a power offset value via RRC, MAC CE or DCI.
7. 7. The method of any of claims 2 to 6 wherein the relay IAB node splits available power between uplink backhaul links and downlink access links by means of one or more of power reservation; power compensation and power scaling.
8. 8. The method of any preceding claim wherein more than one of TDM, FDM and SDM are used simultaneously in a hybrid configuration.
9. 9. The method of claim 8 wherein subframes associated with different multiplexing schemes are divided into multiple sets and different power control schemes are applied to different subframe sets either via explicit configuration or implicitly.