GB2565538A

GB2565538A - Improvements in and relating to semi persistent scheduling in a telecommunication network

Info

Publication number: GB2565538A
Application number: GB1712945.3A
Authority: GB
Inventors: Tesanovic Milos
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2017-08-11
Filing date: 2017-08-11
Publication date: 2019-02-20
Also published as: GB201712945D0

Abstract

A method of performing scheduling which may be semi-persistent in a telecommunications network, comprising the network transmitting to user equipment a primary message, which may be an RRC message or other higher layer message, including at least one transmission parameter for use in communication with the network and a secondary message, which may be a higher or lower layer message and may be a layer 1 message, including at least one of; information regarding selection of a particular option if the at least one parameter includes a plurality of options, and information regarding adjusting the at least one parameter. The user equipment may be preconfigured with information about at least one transmission parameter prior to message receipt. Said at least one parameter can be amended or supplemented by the primary message and/or by the user equipment based on a predefined condition.

Description

Improvements in and relating to semi persistent scheduling in a telecommunication network

The present invention relates to an improved technique for managing and configuring semi persistent scheduling (SPS) in a telecommunication network, or any SPS-like type of scheduling, including, but not limited to, the recently introduced by 3GPP, grant-free, contention-based scheduling. It particularly, but not exclusively relates to New Radio (NR) or Fifth Generation (5G) networks.

SPS is known from, at least, prior art LTE networks. It is used in LTE as a low-overhead scheduling technique for traffic with periodic characteristics. SPS is configured (but not activated) via a higher layer signalling mechanism, (e.g. Radio Resource Control, RRC) which signals the periodicity (using a variable semiPersistSchedlntervalUL). The SPS is then activated via a lower level signalling mechanism (e.g. Physical downlink Control Channel, PDCCH signalling), which enables re-tuning of parameters on a faster basis and with less control signalling overhead, since more frequent messaging such as activation/deactivation/MCS changes is done via lower layer signalling. The joint control of SPS operation by RRC and PDCCH signalling, and the split of information between RRC and PDCCH messages are the two important features of the SPS mechanism in LTE. However, the setup and control of SPS in LTE is rigid and does not allow much if any flexibility in how it is configured.

It has been agreed that 5G (NR) shall support grant-free, SPS-like, Physical Uplink Shared Channel (PUSCH) transmissions. It has been agreed that UL data transmission without UL grant can be configured by the network to be performed after semi-static resource configuration in RRC without Layer 1 (PDCCH) signalling - indicating a departure from how SPS is typically configured and activated, as explained in the previous paragraph in relation to prior art systems.

Nevertheless, uplink SPS, similar to the previously described LTE mode of operation, in which RRC configuration (with no initial PHY resources) is used in tandem with L1 activation/deactivation, will also need to be supported in NR. In effect, NR utilises an LTE-like SPS scheme with L1 activation/deactivation. However, since a common RRC signalling framework for the two (i.e. a scheme which uses L1 activation/deactivation, and a scheme which relies solely on RRC) would be beneficial, embodiments of the present invention aim to provide such a solution.

Therefore, a problem addressed by embodiments of the present invention is how to efficiently implement SPS transmission.

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.

According to an aspect of the present invention, there is provided a method of performing scheduling in a telecommunication network, comprising the steps of: the telecommunication network transmitting to a user equipment a primary message including at least one transmission parameter for use by the user equipment in transmitting to the telecommunication network; the telecommunication network transmitting to the user equipment a secondary message, wherein the secondary message includes at least one of: information regarding selection of a particular option if the at least one transmission parameter includes a plurality of options; and information regarding an adjustment of one of the at least one transmission parameter.

In an embodiment, the user equipment is preconfigured with information concerning at least one transmission parameter prior to receiving the primary message and which the primary message either supplements or amends.

In an embodiment, the user equipment changes one of the at least one of transmission parameter on the basis of a predefined condition.

In an embodiment, the preconfiguring of the user equipment is dependent upon the category or the capabilities of the user equipment.

In an embodiment, the primary message is a higher layer message.

In an embodiment, the higher layer message is an RRC message.

In an embodiment, the secondary message is either a higher or a lower layer message.

In an embodiment, the secondary message is a layer 1 message.

In an embodiment, the scheduling is semi persistent scheduling.

In an embodiment, an uplink transmission instant is determined based on a time when the user equipment receives the primary message.

In an embodiment, the reception time is rounded to one of a predetermined number of candidates on a pre-arranged time grid known to the user equipment and the telecommunication network.

In an embodiment, the predetermined number of candidates lie between a minimum and maximum time, wherein the minimum and maximum times are dependent upon transmission and/or processing delays.

In an embodiment, latency is adjusted by altering a timing between adjacent candidate times.

In an embodiment, statistical analysis the candidate times is performed to determine a distribution of expected transmissions.

In an embodiment, a base station and a user equipment, arranged to perform the method of the preceding aspect.

Embodiments of the present invention may use RRC configuration messages only in a manner different from the one implemented in prior art LTE systems. This may involve using a split of roles between Layer 1 messages and RRC in a manner different from the split implemented in prior art LTE systems.

Embodiments of the present invention are further arranged to change parameters of SPS configuration and to derive the start of the SPS Tx occasion.

Embodiments of the present invention represent a cross between two cases, where the ‘roles’ between RRC and L1 are split, sometimes adaptively.

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 first timeline of candidate times according to an embodiment of the invention; and

Figure 2 shows a second timeline of candidate times according to an embodiment of the invention.

To configure, activate, and reconfigure SPS using RRC signalling only, the RRC messages would need to contain full radio resource configuration (including Modulation Coding Scheme (MCS), frequency/time resource allocations). This is the default situation known in prior art solutions. A major drawback of this is that the signalling load increases, which defeats the purpose of using SPS.

One of the reasons why the signalling load increases is that any change in PHY parameters e.g. MCS (due to channel quality changes, handover, QoS requirements changes etc.) would need to go via RRC signalling every time, originating higher in the stack and involving more layers and/or additional signalling. This clearly increases the overall signalling load.

Another reason why the signalling load increases is that the timing of the grant needs to be determined from the reception ofthe RRC message, which is not straightforward.

In an embodiment of this invention, part ofthe RRC configuration can be made optional, which can then be indicated using Layer 1 signalling, which instruct the UE which option or options to select, as appropriate. A feature of embodiments ofthe present invention is determining how the information split between RRC and Layer 1 signalling is performed. The primary message is sent to the UE via RRC signalling and the secondary message, which adapts or qualifies the information in the primary message may be sent via RRC signalling or L1 signalling. Preferably, L1 signalling is used due to the lower overhead incurred.

One way of performing this is to ensure that the initial RRC message - the primary message contains all the necessary parameters. Some parameters are then changed in pre-defined increments using Layer 1 messages. For example, the periodicity may change based on a codec change, or MCS changes because of codec change (e.g. lower throughput required), or because of poor channel conditions. In other words, at least one transmission parameter provided in the primary message is adjusted on the basis of information provided in the secondary message.

Another way is to ensure that the initial RRC message - the primary message - contains all the necessary parameters. The UE then autonomously changes some ofthe parameters but only when pre-defined triggers, which are also known to the network, occur. Examples of such triggers include: UL channel deteriorates by a certain degree (e.g. below a certain threshold known to the UE and the gNB); UL Tx power becomes limited by a certain degree (e.g. below a certain threshold known to the UE and the gNB).

In another embodiment of this invention, part ofthe RRC message is pre-configured, meaning it is exchanged between the network and the User Equipment (UE) at the start of the communication and can therefore be omitted from RRC signalling. The preconfiguration occurs in advance of any actual communication of voice or data traffic from the UE and may occur, for instance, when the UE registers with the network. The preconfiguration is typically based on UE category/capabilities. For instance, a UE to be used for massive machine type communications (mMTC) applications (e.g. a sensor) which only uses one type of SPS periodicity can have this periodicity pre-configured. Another UE which will always experience good coverage and will not be subjected to handover (e.g. some kind of static measurement sensor) can have a fixed MCS. Taken to the extreme, according to a refinement of this embodiment e.g. a URLLC-only device could have only a single set of pre-programmed parameters, with RRC signalling only used to activate/deactivate SPS.

Various combinations of either of the above techniques may also be used with the first embodiment, described previously.

The split of information between Layer 1 and RRC signalling may be fixed, but it may also be adaptive. For instance, the network can switch to the UE autonomous mode, as set out previously, if the channel conditions are stable and/or if it receives regular and reliable feedback on the DL channel quality. Another scenario is the Time Division Duplex (TDD) mode of operation where reciprocity between UL and DL applies and where UL channel information - known to the network - is used to infer DL channel quality.

As mentioned previously, the derivation of the start time of SPS occasions (without recourse to a L1 activation command) can be a challenging problem. One option is for the network to provide the “co-ordinates” of the first transmission in an RRC message, thereby considerably increasing the signalling load. As an alternative, it could be based on the time when the UE receives the RRC configuration. However, this approach may be problematic, as there will be a transmission and processing delay and so the exact reception time of the RRC configuration may not be known to the gNB.

In embodiments of the present invention, the SPS start time is derived based on the reception time. Further, the reception time is rounded to one of a selected subset of candidates on a preagreed time grid, which is known to both the UE and gNB. This grid can be pre-configured, or it can be shared with the UE as part of the RRC configuration message. This grid is illustrated in Figure 1.

In Figure 1, time is shown on the horizontal axis. Each square 200, 210 forms a candidate transmission time, known to both the UE and the gNB. At a certain time, known to the gNB and represented by the dotted arrow 100, the RRC message is transmitted. Some time later, as represented by solid arrow 110, the RRC message is received by the UE. This time is not known by the gNB.

The candidate time 200 may not be used as the UE has not yet received the message. Any one of candidate times 210 may be used and these will be known to both the UE and the gNB as they form part of a pre-arranged schedule.

Figure 2 shows a more detailed scenario. Since the gNB does not know exactly when its RRC message is received and processed by the UE, the gNB monitors all the UL transmission instants (i.e. a sub-set of pre-agreed candidate times) between [T_sent + delay_min, T_sent + delay_max] and possibly the first one outside this interval, to the right; delay_min and delay_max represent the smallest and largest values of the delay between sending and receiving an RRC message and comprise processing in addition to transmission delay.

The RRC message is transmitted at a time indicated by dotted arrow 300. The UE will receive this at some point between the times mentioned above: T_sent + delay_min, T_sent + delay_max. delay_min is indicated by time period 320. delay_max is indicated by time period 330. The actual time of reception of the RRC message by the UE is indicated by solid arrow 310, and falls in the range defined by [T_sent + delay_min, T_sent + delay_max]. The actual UL transmission will happen at the first such candidate (or at the n^th such candidate, where n is a number configured by the network; n has direct impact on scheduling delay and choosing n=1 is a preferred option, but not the only option) after the actual message reception. In Figure 2, this means that the UL transmission will happen at time 440.

The gNB therefore need not monitor candidate time 400 since this is before T_sent + delay_min and the UE cannot have received the message by this time. The candidate times which the gNB monitors are 410, 420, 430 and 440 since these fall within the range defined by [T_sent + delay_min, T_sent + delay_max]. As mentioned, it may be necessary to also monitor the next candidate 450 falling outside the range, since it is possible that the RRC message is received within the defined range, but the next candidate time falls outside this range. For instance, if the RRC message was received just after candidate time 440, but within time period 300, then the UL transmission will occur at time 450. It will not generally be necessary to monitor the next candidate 460, since this falls too far out of the range.

It may be necessary to limit the number of pre-defined UL candidate transmission instants as they can be considered as wasted because, for instance, no other users can be scheduled in those slots at the same time and frequency, and/or because the gNB needs to monitor them for transmissions which may never happen. This can be done by increasing the spacing between them. However, by doing so scheduling latency is increased.

To address this issue, in an embodiment, the spacing between candidates is made configurable so that a larger spacing is used for applications not requiring low latencies. Furthermore, the decision on whether to make the spacing configurable is based, in an embodiment of the invention, on whether multiple users can be scheduled in the same slot e.g. using MU-MIMO/spatial diversity, thereby alleviating the problem of wasted resources mentioned previously.

In another embodiment, the statistics of the duration of the monitoring interval [T_sent + delay_min, T_sent + delay_max] are monitored. The monitoring interval duration may be defined as: delay_max - delay_min (i.e. the length of the time period in which the RRC message is received at the UE). If the variance of the distribution of this length is low i.e. below a certain predefined threshold, e.g. because reception times tend to cluster strongly around a certain value, e.g. the middle of the interval, or nearer to delay_min), then the spacing of the candidate times can be adjusted to match the expected time of reception. If the variance is high and/or if the fourth moments of the distribution are significant (i.e. the distribution exhibits higher kurtosis, meaning very low and very large values may be expected relatively frequently), then a fixed spacing may be retained to better capture these times.

In a still further embodiment, the monitoring of the grid by the gNB does not start at T_sent + delay_min, but rather at T_sent + delay_p%, where delay_p% is the value of the distribution exceeded in at least a certain percentage of cases. The actual percentage may be set be e.g. 10 or 50% as required. The higher the value of p, the higher the risk that the gNB will miss an UL transmission. However, should the gNB miss an UL transmission, there is a retransmission mechanism in place, which can be used if required. However, reliance on retransmission should be minimised as it incurs a larger scheduling delay. The actual value of p will be a compromise which allows a sufficient number of UL transmissions to be captured, thereby reducing the number of times the network needs to rely on retransmissions as much as possible, without wasting too much time monitoring candidate times which will not, in all likelihood, yield a UL transmission.

The time-grid agreed between UE and gNB can be refined to take into account actual deployment details. To estimate the delay values, delay_max and delay_min, in a further embodiment of this invention, factors such as whether Dual Connectivity (DC) is used, the existence of multiple paths, or if segmentation of RRC messages employed, are taken into account, in the following way:

If the network realises (or so instructs) that the RRC message will be sent via multiple paths (examples include DC but also Carrier Aggregation in case message duplication is used), it revises the delay estimate to take into account the statistics of not one but all affected paths and it includes in its estimate the processing time which is now increased by the need to perform message reassembly

Similarly, if segmentation of RRC messages is employed (for single-path use case), the network takes the additional processing delay into account; should this be combined with multi-path transmission, techniques described previously may be used

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

1. A method of performing scheduling in a telecommunication network, comprising the steps of:

the telecommunication network transmitting to a user equipment a primary message including at least one transmission parameter for use by the user equipment in transmitting to the telecommunication network;

the telecommunication network transmitting to the user equipment a secondary message, wherein the secondary message includes at least one of:

information regarding selection of a particular option if the at least one transmission parameter includes a plurality of options; and information regarding an adjustment of one of the at least one transmission parameter.

2. The method of claim 1 wherein the user equipment is preconfigured with information concerning at least one transmission parameter prior to receiving the primary message and which the primary message either supplements or amends.

3. The method of claim 1 wherein the user equipment changes one of the at least one of transmission parameter on the basis of a predefined condition.

4. The method of claim 2 wherein the preconfiguring of the user equipment is dependent upon the category or the capabilities of the user equipment.

5. The method of any preceding claim wherein the primary message is a higher layer message.

6. The method of claim 5 wherein the higher layer message is an RRC message.

7. The message of any preceding claim wherein the secondary message is either a higher or a lower layer message.

8. The method of claim 7 wherein the secondary message is a layer 1 message.

9. The method of any preceding claim wherein the scheduling is semi persistent scheduling.

10. The method of any preceding claim wherein an uplink transmission instant is determined based on a time when the user equipment receives the primary message.

11. The method of claim 10 wherein the reception time is rounded to one of a predetermined number of candidates on a pre-arranged time grid known to the user equipment and the telecommunication network.

12. The method of claim 11 wherein the predetermined number of candidates lie between a minimum and maximum time, wherein the minimum and maximum times are dependent upon transmission and/or processing delays.

13. The method of claim 12 wherein latency is adjusted by altering a timing between adjacent candidate times.

14. The method of any of claims 10 to 13 wherein statistical analysis the candidate times is performed to determine a distribution of expected transmissions.

15. A system comprising a base station and a user equipment, arranged to perform the method of any preceding claim.