Apparatus, method and computer program for adjustment of subcarrier spacing

Abstract

An adjustment of a subcarrier spacing (SCS) for a multi-carrier communications system, such as Orthogonal Frequency Division Multiplexing (OFDM) in a 5G New Radio system. The modification of the SCS i

Description

TECHNOLOGICAL FIELD Examples of the disclosure relate to apparatuses, methods and computer programs for the adjustment of subcarrier spacing. Some relate to the adjustment of subcarrier spacing in orthogonal frequency-division multiplexing for radio access networks. BACKGROUND Signals can be modulated to aid in the transmission of information. Some modulation schemes, such as orthogonal frequency-division multiplexing (OFDM), use multiple subcarrier signals to allow more information to be transmitted. The subcarriers are modulated to be at different frequencies to one other. The subcarrier spacing (SCS) is the spacing in the frequency domain between the peak frequencies of neighbouring subcarriers. The subcarrier spacing forms part of the numerology defining a signal. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided an apparatus comprising: means for determining an adjustment of a subcarrier spacing for a multicarrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and means for transmitting to at least one user equipment instructions to apply the adjustment to a subcarrier spacing of the multi-carrier communications system. The multi-carrier communications system may comprise a communications channel. Applying the adjustment to the subcarrier spacing of the multi-carrier communications system may comprise applying the adjustment to the subcarrier spacing of the communications channel. The instructions to apply the adjustment to the subcarrier spacing of the multi-carrier communications system may comprise instructions to apply an adjustment of time gaps between symbols. Adjusting time gaps may comprise adding or removing time gaps. The time gaps and subcarrier spacing may be adjusted so that a symbol rate remains substantially the same. Determining an adjustment of the subcarrier spacing may be in dependence upon a comparison of the input bit rate and a physical layer bit rate of the multi-carrier communications system. In some examples, if the input bit rate is within an error margin of the physical layer bit rate the subcarrier spacing is not adjusted; if the input bit rate is more than an error margin below the physical layer bit rate the subcarrier spacing is increased; and if the input bit rate is more than an error margin above the physical layer bit rate the subcarrier spacing is decreased. The physical layer bit rate may be based on a modulation order, an active number of subcarriers, and a symbol duration. The multi-carrier communications system may use orthogonal frequency-division multiplexing, OFDM, to transfer information. The instructions to apply the adjustment to the subcarrier spacing may comprise instructions to the at least one user equipment to enter a load constrained energy saving mode and adjust the subcarrier spacing of the multi-carrier communications system used by the at least one user equipment. The apparatus may further comprise means for receiving from at least one user equipment a load-constrained energy saving request for the at least one user equipment to enter a load-constrained energy saving mode. Entering the load-constrained energy saving mode may comprise adjusting the subcarrier spacing of a multi-carrier communications system used by the at least one user equipment The instructions to apply the adjustment to the subcarrier spacing may specify a new subcarrier spacing. The apparatus may further comprise means for receiving a first transmission from the at least one user equipment with a first subcarrier spacing, and means for receiving a second transmission from the at least one user equipment with a second subcarrier spacing. The first transmission may be received before transmitting the instructions, and the second transmission may be received after transmitting the instructions. The apparatus may further comprise means for determining a second adjustment of the subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. The apparatus may further comprise means for transmitting to the at least one user equipment instructions to apply the second adjustment to the subcarrier spacing of the multi-carrier communications system. The instructions to apply the second adjustment to the subcarrier spacing of the multi-carrier communications system may comprise instructions to the at least one user equipment to exit a load constrained energy saving mode and adjust the subcarrier spacing of the multi-carrier communications system. The may further comprise means for determining an adjustment of a transmission power, discontinuous reception (DRX) cycle, discontinuous transmission (DTX) cycle and / or guard band size in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and means for transmitting to at least one user equipment instructions to apply the adjustment to a transmission power, discontinuous reception (DRX) cycle, discontinuous transmission (DTX) cycle and / or guard band size of the multi-carrier communications system. The apparatus may further comprise means for adjusting the subcarrier spacing of a multi-carrier communications system in dependence upon the received instructions. The subcarrier spacing may be a continuous variable. The apparatus may be a base station. According to various, but not necessarily all, examples there is provided a user equipment comprising: means for receiving instructions to apply an adjustment to a subcarrier spacing of a multi-carrier communications system, and to apply an 4 adjustment of time gaps between symbols in the multi-carrier communications system; and means for adjusting the subcarrier spacing of the multi-carrier communications system and for adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions. The means for adjusting the subcarrier spacing and for adjusting the time gaps between symbols may be configured to adjust time gaps and subcarrier spacing so that a symbol rate remains substantially the same. According to various, but not necessarily all, examples there is provided a method comprising: determining an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and transmitting to at least one user equipment instructions to apply the adjustment to the subcarrier spacing of the multicarrier communications system. According to various, but not necessarily all, examples there is provided a computer program comprising program instructions for causing an apparatus to perform at least the following: determining an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and transmitting to at least one user equipment instructions to apply the adjustment to the subcarrier spacing of the multicarrier communications system. According to various, but not necessarily all, examples there is provided a method comprising: receiving instructions to apply an adjustment to a subcarrier spacing of a multi-carrier communications system, and to apply an adjustment of time gaps between symbols in the multi-carrier communications system; and adjusting the subcarrier spacing of the multi-carrier communications system and adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions. According to various, but not necessarily all, examples there is provided a computer program comprising program instructions for causing an apparatus to perform at least the following: receiving instructions to apply an adjustment to a subcarrier spacing of a multi-carrier communications system, and to apply an adjustment of time gaps between symbols in the multi-carrier communications system; and adjusting the subcarrier spacing of the multi-carrier communications system and adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions. According to various, but not necessarily all, examples there is provided a user equipment comprising: means for transmitting to a base station an energy saving request to enter a load-constrained energy saving mode; means for receiving in response from the base station, instructions to enter the load-constrained energy saving mode wherein the instructions specify a new subcarrier spacing of a multicarrier communications system; and means for entering the load-constrained energy saving mode and adjusting the subcarrier spacing of the multi-carrier communications system to the new subcarrier spacing specified in the received instructions. The apparatus may further comprise means for receiving user input. Transmitting the energy saving request may be based at least in part on receiving the user input. According to various, but not necessarily all, examples there is provided an apparatus for a base station, the apparatus comprising: means for receiving from at least one user equipment a load-constrained energy saving request for the at least one user equipment to enter a load-constrained energy saving mode, wherein entering the load-constrained energy saving mode comprises adjusting a subcarrier spacing of a multicarrier communications system used by the at least one user equipment; and means for transmitting in response, instructions to the at least one user equipment to enter the load constrained energy saving mode and adjust the subcarrier spacing of the multi-carrier communications system used by the at least one user equipment, wherein the instructions specify a new subcarrier spacing of the multi-carrier communications system used by the at least one user equipment. According to various, but not necessarily all, examples there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all of the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all of the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: FIG. 1 shows an example of a network; FIG. 2 shows an example of a signaling chart; FIG. 3 shows an example method for determining an adjustment of a subcarrier spacing; FIG. 4 shows another example of a signaling chart; FIG. 5 shows an example of a chart in which the subcarrier spacing is changed; FIG. 6 shows another example of a chart in which the subcarrier spacing is changed; FIG. 7 shows another example of a signaling chart; FIG. 8 shows an example of a system architecture; FIG. 9 shows an example of numerical results; FIG. 10 shows another example of numerical results; FIG. 11 shows another example of numerical results; FIG. 12 shows an example method; FIG. 13 shows another example method; FIG. 14 shows an example of a controller; and FIG. 15 shows an example of a delivery mechanism. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DEFINITIONS 3GPP Third Generation Partnership Project 5G 5th Generation Al Artificial Intelligence BER Bit error rate CP Cyclic prefix CSI Channel state information DRX Discontinuous reception DTX Discontinuous transmission EE Energy efficiency E-UTRAN Evolved Universal Terrestrial Radio Access Network FPGA Field-Programmable Gate Array gNB 5G / NR base station ICI Inter-Carrier-Interference ISI Inter-Symbol-lnterference LS Least squares LTE Long-Term Evolution MIB Master Information Block ML Machine Learning NG-RAN Next Generation Radio Access Network NR New Radio OFDM Orthogonal frequency-division multiplexing PA Power amplifier PAPR Peak-to-average-power ratio PUSCH Physical Downlink Control Channel PUSCH Physical Uplink Shared Channel RAN Radio Access Network RF Radio Frequency RRC Radio Resource Control Rx Receive SCS Subcarrier Spacing Tx Transmit UE User Equipment uRLLC Ultra-Reliable Low Latency Communication DETAILED DESCRIPTION FIG. 1 illustrates an example of a network 100 comprising a plurality of network nodes including terminal nodes 110, access nodes 120 and one or more core nodes 129. The terminal nodes 110 and access nodes 120 communicate with each other. The one or more core nodes 129 communicate with the access nodes 120. The network 100 is in this example a radio telecommunications network, in which at least some of the terminal nodes 110 and access nodes 120 communicate with each other using transmission / reception of radio waves. The one or more core nodes 129 may, in some examples, communicate with each other. The one or more access nodes 120 may, in some examples, communicate with each other. The network 100 may be a cellular network comprising a plurality of cells 122 each served by an access node 120. In this example, the interface between the terminal nodes 110 and an access node 120 defining a cell 122 is a wireless interface 124, and the nodes 110, 120, 129 are wireless network nodes. The access node 120 is a cellular radio transceiver. The terminal nodes 110 are cellular radio transceivers. In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE) and the access nodes 120 are base stations. In the particular example illustrated the network 100 is an Evolved Universal Terrestrial Radio Access network (E-UTRAN). The E-UTRAN consists of E-UTRAN NodeBs (eNBs) 120, providing the E-UTRA user plane and control plane (RRC) protocol terminations towards the UE 110. The eNBs 120 are interconnected with each other by means of an X2 interface 126. The eNBs are also connected by means of the S1 interface 128 to the Mobility Management Entity (MME) 129. In other example the network 100 is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs) 120, providing the user plane and control plane (RRC) protocol terminations towards the UE 110. The gNBs 120 are interconnected with each other by means of an X2 / Xn interface 126. The gNBs are also connected by means of the N2 interface 128 to the Access and Mobility management Function (AMF). A user equipment 110 comprises a mobile equipment. Where reference is made to user equipment 110 that reference includes and encompasses, wherever possible, a reference to mobile equipment. Energy efficiency (EE) is crucial for design and development of radio access networks, including for 6G. Cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) is the main waveform for 5G NR and is also one of the main waveform candidates for 6G. CP-OFDM suffers from high power amplifier (PA) backoff induced by large peak-to-average power ratio (PAPR). This leads to lower efficiency of the PA. The lower efficiency of PA directly affects the energy efficiency of the network. To counteract this, current approaches involve PAPR reduction methods to improve the EE at the expense of increased computational complexity, signaling overhead, and bit error rate (BER). A numerology refers to a specific subcarrier spacing (SCS) and cyclic prefix (CP) length. Numerology of waveforms significantly affects the achievable throughput as well as the PAPR, and consequently, the energy efficiency of the network. An increase in SCS leads to a reduction in the PAPR and, consequently, an increase in the energy efficiency. FIG. 2 shows an example signaling chart according to examples of the disclosure. The signaling chart shows a user equipment 110 and a network node 120. The network node 120 may be an access node 120 as illustrated in FIG. 1, and can be a base station 120 such as a gNB 120. A system can comprise the user equipment 110 and the network node 120. At block 210, the network node 120 determines an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. The change of an input bit rate for transfer via the multi-carrier communications system may be an input bit rate from the user equipment 110, such as from the user equipment 110 to the network node 120. The input bit rate may be the number of bits that need to be transmitted within a given period of time. The multi-carrier communications system comprises at least one transmitter, at least one receiver and at least one communications channel. The at least one transmitter transmits signals across the communications channel to the at least one receiver. The at least one transmitter is present in the user equipment 110 and / or the network node 120. The at least one receiver is present in the user equipment 110 and / or the network node 120. The communications channel carries or comprises one or more transmissions. In some examples, adjustment of a subcarrier spacing of the multi-carrier communications system may be adjustment of a subcarrier spacing of multiple subcarrier spacings associated with the multi-carrier communications system. In some examples, the multi-carrier communications system uses orthogonal frequency-division multiplexing, OFDM, to transfer information such as data and / or control information. In some examples, the multi-carrier communications system uses cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM). At block 220, the network node 120 transmits to the user equipment 110 instructions 225 to apply the adjustment to a subcarrier spacing of the multi-carrier communications system. In some examples, the instructions 225 specify a new subcarrier spacing to be applied. However, in other examples the instructions 225 do not specify the new subcarrier spacing. In some examples, at least one user equipment 110 transmits the adjustment instructions 225 to more than one user equipment 110. At block 230, the user equipment 110 receives the instructions 225 to apply an adjustment to a subcarrier spacing of the multi-carrier communications system. At block 240, the user equipment 110 adjusts the subcarrier spacing of the multi-carrier communications system in dependence upon the received instructions 225. In some examples, the network node 120 adjusts the subcarrier spacing of the multicarrier communications system in dependence upon the received instructions 225. Applying the adjustment to a subcarrier spacing of the multi-carrier communications system can comprise applying the adjustment to a subcarrier spacing of the at least one transmitter, at least one receiver and / or the at least one communications channel. In some examples, the subcarrier spacing is a continuous variable which can be set to substantially any value, or substantially any value within a range of values. In other examples, the subcarrier spacing is a discrete variable which can only be set to certain values. In some examples, determining an adjustment of a subcarrier spacing, as in block 210 in FIG. 2, is in dependence upon a comparison of the input bit rate and a physical layer bit rate of the multi-carrier communications system. FIG. 3 shows an example method 300 which corresponds to an example of this determination. At block 310, the network node 120 obtains an input bit rate value Rjn. In some examples the network node 120 receives the input bit rate from the at least one user equipment 110. At blocks 320 and 340, the network node 120 compares of the input bit rate and the physical layer bit rate. In this example, the physical layer bit rate is based on a modulation order Qm, an active number of subcarriers Nact, and the time period between consecutive symbols Tsym. Specifically in this example, the physical layer bit rate is given by (Qm* Nact) I Tsym. The network node 120 may receive some or all of these parameters from the user equipment 110. In this example an error margin 8m is used in the comparison of the input bit rate and the physical layer bit rate. This helps to ensure that subcarrier spacing is not changed repeatedly due to small fluctuations in the input bit rate, and so reduces the use of network resources. In other examples, an error margin is not used. At block 320, if the input bit rate is within an error margin of the physical layer bit rate the method proceeds to block 330 where the subcarrier spacing is not adjusted and remains, at least substantially, the same. Thus, if the input bit rate is smaller than the physical layer bit by a first error margin, or is bigger than the physical layer bit by a second error margin, the subcarrier spacing is not adjusted. In this example the first and second error margins are the same, however in other examples the first and second error margins are different. If the input bit rate is outside of the error margin of the physical layer bit rate the method proceeds to block 340. At block 340, if the input bit rate is more than the second error margin above the physical layer bit rate, the method proceeds to block 360 where the subcarrier spacing is decreased. If the input bit rate is more than the first error margin below the physical layer bit rate, the method proceeds to block 360 where the subcarrier spacing is increased. From the blocks 330, 350 and 360, the method proceeds to block 370. In block 370 a resource grid mapper performs physical resource block mapping, and maps the data symbols to a resource element for one or more transmission(s) over the communication channel. This can comprise adjusting the subcarrier spacing of the multi-carrier communications system. A resource element is the smallest unit of a resource grid comprises one subcarrier in the frequency domain and one OFDM symbol in the time domain. Increasing subcarrier spacing leading to a reduction in the PAPR and, consequently, an increase in the energy efficiency. However, increasing subcarrier spacing might potentially be undesirable at higher load levels due to decreasing the throughput and increasing interference. When load is low, e.g. when input bit rate is lower than the physical layer bit rate, the subcarrier spacing (SCS) is increased to improve energy efficiency. When load is high, e.g. when input bit rate is input bit rate is higher than the physical layer bit rate, the SCS is increased to improve throughput. Therefore a technical effect of this disclosure is in optimizing subcarrier spacing of the multicarrier system with respect to energy efficiency, throughput, and interference. The at least one user equipment 110 applying an adjustment to increase a subcarrier spacing may form at least part of the at least one user equipment 110 entering a load constrained energy saving mode. Instructing the at least one user equipment 110 to apply the adjustment to increase a subcarrier spacing may form at least part of instructing the at least one user equipment 110 to enter the load constrained energy saving mode. Similarly, the at least one user equipment 110 applying an adjustment to decrease a subcarrier spacing may form at least part of the at least one user equipment 110 exiting the load constrained energy saving mode. As well as subcarrier spacing, a number of other parameters can be adjusted to improve energy efficiency. For example, adjusting transmission power, discontinuous reception (DRX) cycle, discontinuous transmission (DTX) cycle and / or guard band size. In some examples, the network node 120 determines an adjustment of a transmission power, DRX cycle, DTX cycle and / or guard band size in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. This can be part of the same determination of an adjustment of a subcarrier spacing of block 210, and can be considered to together form a decision of entering or exiting a load constrained energy saving mode. The network node 120 can transmit to at least one user equipment 110 instructions to apply the adjustment to a transmission power, DRX cycle, DTX cycle and / or guard band size of the multi-carrier communications system. The instructions may form part of the instructions 225 to apply an adjustment to a subcarrier spacing of the multicarrier communications system, and may form part of instructions 225 to enter or exit the load constrained energy saving mode. FIG. 4 shows an example signaling chart according to examples of the disclosure. The signaling chart of FIG. 4 can comprise some or all of the features of the signaling chart of FIG. 2. The user equipment 110 transmits a first transmission 405 with a first subcarrier spacing. The network node 120 then receives the first transmission 405 from the user equipment 110. At block 210, the network node 120 determines an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. This can be the determination as shown in FIG. 3. The network node 120 determines an adjustment of a subcarrier spacing to a second subcarrier spacing, which is a new subcarrier spacing. The network node 120 transmits to the user equipment 110, instructions 225 to apply the adjustment to the second subcarrier spacing of the multi-carrier communications system. The user equipment 110 then receives these instructions 225. In some examples, the network node 120 transmits the instructions 225 using the first subcarrier spacing. At block 240, the user equipment 110 adjusts the subcarrier spacing of the multi-carrier communications system to the second subcarrier spacing in dependence upon the received instructions 225. The user equipment 110 transmits at least a second transmission 455-1 with the second subcarrier spacing. In this example, the user equipment 110 transmits multiple transmissions 455-1 to 455-n with the second subcarrier spacing. The network node 120 then receives the second transmission(s) 455-1, 455-n from the user equipment 110. The first transmission 405 is transmitted by the at least one user equipment 110 and received by the network node 120 before the instructions 225 are transmitted by the network node 120 and received by the at least one user equipment 110. The second transmission 445 is transmitted by the at least one user equipment 110 and received by the network node 120 after the instructions 225 are transmitted by the network node 120 and received by the at least one user equipment 110. At block 450, the network node 120 determines a second adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. This may be substantially the same as the determination process as in block 210, and the determination as shown in FIG. 3. The network node 120 determines an adjustment of a subcarrier spacing to a third subcarrier spacing. The network node 120 transmits to the user equipment 110 instructions 455 to apply the adjustment to the third subcarrier spacing of the multi-carrier communications system. The user equipment 110 then receives these instructions 455. In some examples, the network node 120 transmits the instructions 455 using the second subcarrier spacing. At block 460, the user equipment 110 adjusts the subcarrier spacing of the multi-carrier communications system to the third subcarrier spacing in dependence upon the received instructions 455. In some examples, the third subcarrier spacing is substantially the same as the first subcarrier spacing. In these examples, adjusting the subcarrier spacing to the third subcarrier spacing can be considered to be reverting the subcarrier spacing to its previous value; and the instructions 455 to apply the adjustment to the third subcarrier spacing can be considered instructions 455 to revert the subcarrier spacing to its previous value. In other examples, the third subcarrier spacing is different to the first subcarrier spacing. The user equipment 110 transmits at least a third transmission 465 with the third subcarrier spacing. The network node 120 then receives the third transmission(s) 465 from the user equipment 110. In some examples, the network node 120 transmits subsequent instructions to the user equipment 110 using the third subcarrier spacing. In some examples, the transmissions 405, 445, 465 from the user equipment 110 are Physical Uplink Shared Channel (PUSCH) transmissions 405, 445, 465, and the transmissions 225, 455 from the network node 120 are Physical Downlink Control Channel (PDCCH) transmissions 225, 455. In some examples, the subcarrier spacing is configured by a Master Information Block (MIB) 225, 455 which may be transmitted periodically over Physical Broadcast Channel (PBCH). In some examples, the subcarrier spacing is specified in the parameter “subCarrierSpacingCommon” in the MIB 225, 455. In some examples, the determinations 210, 450 of whether to change subcarrier spacing occur periodically, such as with a period of 20 ms, or 100 ms. In some examples, the determinations 210, 450 of subcarrier spacing occur in response to a trigger, for example in response to received and / or transmitted messages between the network node 120 and user equipment 110. In some examples, the time period between transmitting to at least one user equipment 110, instructions 225 to apply the first adjustment to a first subcarrier spacing and transmitting to at least one user equipment 110, instructions 455 to apply the second adjustment to a second subcarrier spacing is less than 500 ms. FIG. 5 shows an example of changing the subcarrier spacing 501, 511, 521. In this example four symbols 506, are transmitted, 00, 01, 10 and 00. In (a) a first subcarrier spacing 501 is used. In this example, the load is low and two subcarriers 502 are active, with six subcarriers 502 being inactive. First, a first symbol 506 is transmitted over a first subcarrier 502 and a second symbol 506 is transmitted over a second subcarrier 502. Next a third symbol 506 is transmitted over the first subcarrier 502 and a fourth symbol 506 is transmitted over the second subcarrier 502. The subcarrier spacing 501 is the extent a subcarrier 502 extends in the frequency domain. The symbol duration 504 is the extent a symbol 506 extends in the time duration. In (a) no time gaps 508 are present between symbols 506. In (b) a second subcarrier spacing 511 is used which is double the first subcarrier spacing 501. The load remains substantially the same. This doubling of subcarrier spacing 511 means that there are four total subcarriers 502, two inactive and two active. The doubling of subcarrier spacing 511 also causes the symbol duration 504 to halve. In this example, time gaps 508 are present between consecutive symbols 506. However in other examples, time gaps 508 are not present. The time gaps 508 in (b) are substantially the same size as the symbol duration 504. Thus, the symbol rate remains substantially the same between (a) and (b). In (c) a third subcarrier spacing 521 is used which is double the second subcarrier spacing 511. The load remains substantially the same. This doubling of subcarrier spacing 521 means that there are two total subcarriers 502, both of which are active with no inactive subcarriers present. The doubling of subcarrier spacing 521 again causes the symbol duration 504 to halve In this example, the time gaps 508 in (c) are larger than in (b). The time gaps 508 in (c) are substantially four times the size of the symbol duration 504. Thus, the symbol rate remains substantially the same between (b) and (c). The network node 120 may transmit instructions to the user equipment 110 to apply an adjustment of time gaps 508 between symbols 506. In some examples these instructions are part of the instructions 235 to apply the adjustment to a subcarrier spacing 501,511, 521. In other examples they may be separate instructions. Adjusting time gaps 508 can comprise adding, removing, increasing, and / or decreasing time gaps 508. In some examples, the time gaps 508 and subcarrier spacing 501, 511, 521 are adjusted so that the symbol rate remains substantially the same. In some examples, the time gaps 508 and subcarrier spacing 501, 511, 521 are adjusted so that the time period between the start of consecutive symbols 506 is substantially the same. In some examples, the time gaps 508 and subcarrier spacing 501, 511, 521 are not adjusted to cause the symbol rate to remain substantially the same, and different time gaps 508 are used. As subcarrier spacing 501, 511, 521 increases there is higher inter-symbol-interference (ISI). The time gaps 508 reduce the inter-symbol-interference. FIG. 6 shows another example of changing the subcarrier spacing 501, 511. In (a) a first subcarrier spacing 501 is used. In this example, the load is low and four subcarriers 502 are active, In (a) time gaps 508 are present between consecutive symbols 506. The illustrated time gaps 508 are substantially the same size as the symbol duration 504. In (b) a second subcarrier spacing 511 is used which is double the first subcarrier spacing 501. The load remains substantially the same. This doubling of subcarrier spacing 511 means that there are two active subcarriers 502, and causes the symbol duration 504 to halve. The time gaps 508 in (b) are substantially the same size as the symbol duration 504. Thus, the symbol rate remains substantially the same between (a) and (b). In this example a higher subcarrier spacing 511 is used in a low-load case. This has the effect of reducing PAPR and so increasing energy efficiency. ISI is mitigated by maintaining time gaps 508 between symbols 506, which is made possible by the low load. In both (a) and (b) the illustrated time gaps 508 may be considered to make it so that only every other symbol 506 is used. Machine learning (ML) based receivers, such as DeepRX receivers, have the potential to compensate for different signal impairments such as delay spread, doppler shift, phase noise, and frequency selectivity of the channels. In examples of the disclosure, new numerology increases the EE of the network while the ML based receiver compensates for other impairments that are imposed by the new numerology. DeepRX is a deep fully convolutional neural network (CNN) which can receive the frequency domain signal over the whole transmission time interval (TTI), and outputs the log-likelihood ratios (LLRs) of the transmitted bits. As such, it can estimate the transmitted signal based on the received frequency domain signal. As DeepRx is trained to operate under various different scenarios, parameters and configurations, it is robust against the impairments in the received signal. The operation of 5G and 6G networks over a wide spectrum range can use flexible numerology to deal with different service-specific requirements, e.g., ultra-low energy for large scale Internet of Things, as well as several propagation conditions imposed by different frequency bands. Increasing subcarrier spacing (SCS) 501, 511, 521 leads to a reduction in the PAPR and, consequently, an increase in the energy efficiency. This reduction occurs because wider subcarriers 502 result in a decreased number of subcarriers 502 within the available bandwidth, which results in a lower dynamic range of the time-domain OFDM signal. On one hand, increasing SCS 501, 511, 521 provides more resilience to inter-carrier-interference (ICI) which becomes more significant at higher carrier frequency, as well as in high-mobility scenarios due to the larger Doppler shift. Furthermore, it is a promising choice for ultra-reliable low latency communication (uRLLC) services with stringent requirements on latency. On the other hand, because CP length can be a fixed portion of the symbol duration 504, a larger SCS 501, 511, 521 results in higher inter-symbol-interference (ISI) due to shorter CP length. In cases of excessive delay spread (larger than CP length), advanced receivers, such as DeepRx, can be used to mitigate the effect of ISI. This may be important in examples where load is high, and there might not be space for time gaps 508 between consecutive OFDM symbols 506 whilst maintaining throughput. One option is to select a common fixed CP length for different subcarrier spacings 501, 511, 521. However, this will result in misalignments on the slot boundaries. The number of users, use cases, and services expected to be supported by 6G radio access technologies is increasing drastically. More flexibility in waveform numerologies can address different requirements on energy efficiency, latency, spectral efficiency, and resiliency against different impairments. Receivers may have poor flexibility in detecting the signal in case of increased ISI induced by increasing the SCS 501, 511, 521. Because the CP length is a fixed T proportion of the symbol duration 504 (Tcp = the increased SCS 501, 511, 521 leads to a shorter CP duration which results in more ISI and performance degradation. The increased ISI also complicates the equalization for frequency selective channels. On the other hand, over-increasing the CP duration to cope with larger SCS 501, 511, 521 will degrade the system spectral efficiency and increase the latency. Moreover, varying CP duration with SCS 501,511, 521 causes a mismatch on slot boundaries of OFDM symbols 506. This disclosure proposes a more energy efficient flexible numerology for 6G which dynamically adapts SCS 501, 511, 521 based on the traffic load, or on a user request. As a result, a larger SCS 501, 511, 521 is opted for more energy saving in low traffic scenarios, or upon the request from users to switch to an energy saving mode. The increased SCS 501, 511, 521 results in more EE because by increasing the SCS 501, 511, 521, fewer subcarriers 502 are used within a given spectrum, the PAPR will be smaller because fewer subcarriers 502 are combined to construct the multi-carrier OFDM waveform. Lower PAPR results in higher PA efficiency and, thus, more EE. For low load scenarios, the effect of larger ISI will be rather minimal because the same amount of data can be multiplexed over a shorter symbol duration 504 when increasing the SCS 501, 511, 521. Thus, because the data is sent over a shorter slot, there will be time gaps I temporal breaks 508 between consecutive symbols 506 which contribute to ISI reduction. The flexible numerology proposed herein may make use of ML receivers, such as DeepRX to shape Al-native air interface for 6G. AML receiver, with the great capability to learn, has a great potential to harness the benefits of larger SCS 501, 511, 521, i.e., more resilience to ICI, lower PAPR, and, consequently, higher EE, while reducing its drawbacks, i.e., larger ISI. The following advantages are provided by some embodiments: • The proposed flexible numerology is more compatible with 6G’s wider spectrum range. • The new numerology has better performance in terms of PAPR and EE. • For low load scenarios, more EE can be achieved without compromising on throughput. • The flexible numerology does not rely on any PAPR reduction techniques to increase energy efficiency. Thus, it reduces the computational and signaling complexity caused by most of the PAPR reduction methods. • Time gaps between symbols reduce ISI. The energy efficiency of a multicarrier OFDM system can be given by the following equation: _ Em=i En=i ^m,n*(l~BER) 'lofdm — yM yN „ / „ ’ o' Z.m=i Mi=i Pm,n / 'Ipa where N is the number of active subcarriers 502, M is the number of symbols 506, Rm n is the per symbol rate for subchannel n, BER is the bit error rate, and pmn is the per symbol transmission power, respectively. As can be seen from the Eq. (1), energy efficiency is directly proportional to the BER and the PA’s efficiency T]pa. The BER is affected by both ISI and ICI. The higher SCS 501, 511, 521 results in less ICI but more ISI due to shorter CP. The parameter T]pa increases with increasing SCS 501, 511, 521 due to lower PAPR and, consequently, lower PA backoff. By increasing the SCS 501, 511, 521 in situations of low loads (low input bit rate), the system can multiplex the same amount of data on fewer subcarriers 502 over a smaller symbol duration 504 (because it is inversely proportional to the SCS 501, 511, 521). Because there are many null subcarriers in case of having low load, data is distributed over more frequency resources and fewer time resources without requiring additional spectrum but by utilizing the null subcarriers. Although reduced PAPR and increased EE is the primary benefit of increasing the SCS 501, 511, 521, the fact that the data is sent over a shorter period of time further contributes to mitigate increased ISI induced by larger SCS 501, 511, 521. An example in a low load scenario is illustrated in FIG. 5. Assuming that the input bit rate is 4 bits per Tsvm where Tsvm is the symbol duration 504 corresponding to the SCS 501 chosen for FIG. 5(a); and assuming the total number of subcarriers 502 to be 8 and 4-QAM as the modulation scheme, there will be 6 null subcarriers. In FIG. 5(a), the symbols 506 are sent consecutively without any time gaps 508 between them. This might cause ISI if the CP duration is smaller than the maximum delay spread of the channel. In FIG. 5(b), the SCS 511 is doubled, which results in occupying more frequency resources (subcarriers 502) while sending the data over half of the time as in the Tsym. Tsym. previous case (FIG 5(a)), i.e., —There will be —time gaps 508 between consecutive symbols 506 which can mitigate ISI caused by increased SCS 511. In FIG. 5(c), the SCS 521 is four times larger than in FIG. 5(a) and all frequency Tsym. resources, subcarriers 502, are occupied while the data is seat over — arid there 3 TSym are-----1 time gaps 508 between symbols 506. 4 In this example, the time gaps 508 have no effect on the latency because the summation of the new symbol duration 504 and the time gap 508 is equal to the symbol duration 504 as in the scenario a) with a lower SCS 501. We can see that in this example, the increase in the SCS 501, 511, 521 corresponds directly to the increase in the time gap 508 between consecutive symbols 506, which helps counteracting the negative effect of increased SCS 501, 511, 521, i.e., more ISI. Implementing this same approach when having moderate or high load, however, results in lower throughput given the same number of resource blocks and modulation order. For a higher load scenario, the throughput (achievable bit rate at the receiver) decreases with increasing the subcarrier spacing 501, 511, 521. The reason for this is the increased inter-symbol-interference (ISI) due to the decreased cyclic prefix duration because it is inversely proportional to the SCS 501, 511, 521. Lower load allows time gaps 508 between the consecutive symbols 506 in time, which remedies the increased ISI caused by increased SCS 501, 511, 521. In some examples, increasing SCS 501, 511, 521 decreases the throughput in case of high load but does not change the transmit bit rate. An adaptive SCS 501, 511, 521 selection scheme based on load level is disclosed. The decision on the selection of the SCS 501, 511, 521 is based on the input bit rate, modulation order, active number of subcarriers 502, and symbol duration 504 denoted by Rin. Qm. Nact, and Tsym, respectively. The modulation order is the number of bits that can be modulated by a symbol 506 in a constellation. On a (sub)frame, the resource grid mapper 370 receives an update on the SCS 501, 511, 521 value. Based on the physical layer bit rate and the input bit rate which represents the load level, a decision is made to either increase, decrease, or keep the same SCS 501, 511, 521. The resource grid mapper 370 will be updated by the decision. The flowchart depicted in FIG. 3 illustrates an example of how the adaptive SCS 501, 511, 521 selection can be implemented based on the input load level. The parameter em is the error margin which is added to reduce undesired SCS 501, 511, 521 switching due to small fluctuations in load level. The signaling of the selected SCS 501, 511, 521 can be done as shown in FIG. 4 for uplink. In this example case, the network node I gNB 120 detects a sufficiently low load for favoring energy efficiency instead of throughput. In order to signal the information to the UE 110, a high-EE mode can be defined. It includes certain adjusted parameters related to the waveform numerology, including higher SCS 501, 511, 521, and potentially including discontinuous reception (DRX) cycle, discontinuous transmission (DTX) adaptation, and adjusted power control parameters for reducing TX power. In one embodiment, the SCS 501, 511, 521 is selected following the procedure of FIG. 3, and if a higher SCS 501, 511, 521 is determined, the network node 120 invokes a high-EE mode. The selected SCS 501, 511,521 is then signaled as a parameter along with the signaling of the any other high-EE parameters. The new SCS 501, 511, 521 is signaled to the UE 110 in a modified scheduling grant 225, which may comprise an indicator for the SCS 501, 511, 521 to be used. Once the UE 110 receives the scheduling grant 225, it will also receive information regarding which SCS 501, 511, 521 should be used. The network node 120 can include this indication to substantially all scheduling grants or it can be included only when the SCS 501, 511, 521 changes. If the load increases, a similar procedure can be used to instruct UEs 110 to start using a lower SCS 501, 511, 521. In another embodiment, information concerning the SCS 501, 511, 521 can be signaled also as an explicit control message 225, or as a part of another standard message 225. The procedure for downlink follows similar logic, with the information concerning SCS 501, 511, 521 being either part of the scheduling information or as a separate control message. Other than the load-based decision-making process shown in FIG. 3, the decision to alter the subcarrier spacing 501, 511, 521 can be also triggered upon a user request to switch to an energy saving mode at the expense of having less throughput. The network node 120 can decide if a target throughput can be achieved in the high-EE mode and calculate the new parameters (specifically a larger SCS 501, 511, 521) considering the channel condition and the velocity of the user equipment 110. This scenario may occur for moderate / high load level when the conditions given in FIG. 3 have not been met to switch to a higher SCS 501, 511, 521. An example signal diagram for this case is illustrated in 7. The signaling chart of FIG. 7 can comprise some or all of the features of the signaling charts of FIG. 2 and FIG. 4. The procedure of FIG. 7 is largely similar to that illustrated in FIG. 4 where the network node 120 controls the entry into, and exit from, the energy saving mode. However, in the example of FIG. 7 the initiative comes from the UE 110 request 715. The UE 110 can include the request 715 in its UL scheduling request. If the network node 120 accepts the request 715, it can calculate the parameters (including the larger SCS 501, 511, 521) and signal it to the UE 110 in the scheduling grant 725. In some examples the request 715 is not accepted, and regular mode will be used in the future transmissions 445, with the subcarrier spacing 501, 511, 521 unchanged. At block 710, the user equipment 110 decides to request to enter an energy saving mode. This decision may be in response to user input. The user equipment 110 then transmits an energy saving request 715 to enter a load-constrained energy saving mode; wherein entering the load-constrained energy saving mode comprises adjusting a subcarrier spacing 501, 511, 521. Adjusting the subcarrier spacing 501, 511, 521 may comprise adjusting the subcarrier spacing 501, 511, 521 for a user equipment 110, for a plurality of user equipment 110 which may be a subset of all user equipment 110, and / or for some resources of a multi-carrier communications system. At block 720, the network node 120 determines whether to accept the request 715 to enter the energy saving mode. The network node 120 may determine an adjustment of a subcarrier spacing 501 to a second subcarrier spacing 511. The network node 120 transmits, to the user equipment 110, instructions 725 to enter an energy saving mode. The instructions 725 may specify the second subcarrier spacing 511. The instructions 725 are transmitted in response to receiving the request 715. At block 240, the user equipment 110 enters the energy saving mode and adjusts the subcarrier spacing 501 of the multi-carrier communications system to the second subcarrier spacing 511 in dependence upon the received instructions 725. The user equipment 110 transmits at least a second transmission 455-1 with the second subcarrier spacing 511. In this example the user equipment 110 transmits multiple transmissions 455-1 to 455-n with the second subcarrier spacing 511. At block 750, the user equipment 110 decides to request to exit the energy saving mode. This decision may be in response to user input. The user equipment 110 then transmits the request 755 to exit the load-constrained energy saving mode; wherein exiting the load-constrained energy saving mode comprises adjusting a subcarrier spacing 511. At block 760, the network node 120 determines whether to accept the request 755 to exit the energy saving mode. The network node 120 may determine an adjustment of a subcarrier spacing 511 to a third subcarrier spacing 521. In some examples the third subcarrier spacing 521 is the first subcarrier spacing 501. The network node 120 transmits to the user equipment 110 instructions 765 to exit the energy saving mode. At block 460, the user equipment 110 adjusts the subcarrier spacing 511 of the multicarrier communications system to the third subcarrier spacing 521 in dependence upon the received instructions 765. In some examples, the transmissions 715, 445, 765, 465 from the user equipment 110 are Physical Uplink Shared Channel (PUSCH) transmissions, and the transmissions 725, 755 from the network node 120 are Physical Downlink Control Channel (PDCCH) transmissions. Numerical Results The numerical results compare the performance of three different SCS 501, 511, 521, i.e., 30, 60, and 120 kHz in terms of BER and PAPR. Three types of receivers are considered for the simulations which are baseline with least squares (LS) estimator 810, baseline with perfect channel state information (CSI) 820, and DeepRX 830. The 27 schematic architecture of the end-to-end OFDM transmitter and the three receivers 810, 820, 830 are shown in FIG. 8. The architecture comprises: a binary sources 802, an encoder 804, a mapper 806, a resource grid mapper 370, a wireless channel 808 and the three receivers 810, 820, 830. The first receiver 810 is a baseline with least squares (LS) estimator receiver 810. It comprises a linear minimum mean squared error equalizer 812, a LS channel estimator 814, a demapper 816 and a decoder 818. The second receiver 820 is a baseline with perfect channel state information receiver 820. It comprises a linear minimum mean squared error equalizer 822, a demapper 824 and a decoder 826. The third receiver 830 is DeepRX receiver 830. Simulation parameters for the performed simulations are summarized in Table 1. Simulation parameters Value Carrier frequency 2.6 GHz Channel Model CDL ['B','C','D'] for training, CDL ['A','B'] for validation Delay spread [500 - 600] ns, [2 - 5] ps Velocity 5, 35 m / s SNR range [5 - 35] dB Number of PRBs 16, 8, 4 Subcarrier spacing (SCS) 30, 60, 120 kHz TTI length 14 symbols Modulation scheme 64QAM Table 1. Simulation parameters Effect of SCS on the PAPR: The effect of different SCSs 501, 511, 521, i.e., 30, 60, 120 kHz on the PAPR is shown in FIG. 9 by the complementary cumulative distribution function (CCDF) values. For larger SCSs 501, 511, 521 fewer subcarriers 502 are combined within a symbol duration 504 to construct the multi-carrier OFDM waveform which results in much lower PAPR. As can be seen in FIG. 9, the PAPR reduction is more significant when switching from 60 kHz to 120 kHz compared to the transition from 30 kHz to 60 kHz. The PAPR reduction will impact the PA’s back off and efficiency and, consequently, there will be a gain in overall energy efficiency. Effect of velocity on BER: FIG. 10 shows the effect of different SCS 501, 511, 521 on BER with delay spread ranging between 500 ns and 600 ns. We can observe from the figures that for all of the tested SCSs 501, 511,521, i.e., 30, 60, and 120 kHz, DeepRX 830 outperforms the baseline receivers 810, 820. In addition, DeepRX 830 exhibits the same or superior performance with higher SCS 501, 511,521 as the baseline receivers 810, 820 with lower SCS 501, 511, 521. For instance, in FIG. 10 (a), for maximum velocity of 5 m / s, DeepRX 830 with SCS = 60 kHz outperforms baseline 810, 820 with SCS = 30 kHz. Moreover, DeepRX 830 with SCS = 120 kHz slightly outperforms baseline 810, 820 with SCS = 60 kHz for SNR <20 dB. In FIG. 10(b), by increasing the velocity to 35 m / s, as more severe Doppler shift causes more ICI, we can observe a performance degradation which is very mild for both DeepRX 830 and CSI receiver 820, and more severe for the LS receiver 810. We can see from FIG. 10(b) that DeepRX 830 with SCS = 60 kHz considerably outperforms LS receiver 810 with SCS = 30 kHz. For SCS = 120 kHz, DeepRx 830 exhibits almost the same performance as the baseline 810, 820 with SCS = 30 and 60 kHz. In addition, the greater resilience of larger SCS against higher ISI can be also seen from FIG. 10 when SCS = 120 kHz. Effect of delay spread on BER: FIG. 11 compares the effect of different SCS 501, 511, 521 on BER for maximum velocity is set to 35 m / s when delay spread ranges between [500 - 600] ns (a) and [2 - 5] ps (b). For delay spread between [2 - 5] ps, CP duration which is set to is barely enough to mitigate ISI which justifies the BER degradation compared to the case of having [500 - 600] ns delay spread range. In FIG. 11(b), it can be observed that DeepRX 830 with SCS = 60 kHz exhibits almost the same performance as the baseline receivers 810, 820 with SCS = 30 kHz and even slightly better for SNR <20 dB. For SCS = 120, DeepRX 830 outperforms the baseline receivers 810, 820 with SCS = 30, 60 kHz. Based on the numerical results, it can be concluded that adaptive numerology can be utilized for more energy saving. The following concluding remarks can be highlighted based on the given results: • For moderate / high load scenarios, it can be concluded that DeepRX 830 can handle the increased ISI caused by increased SCS 501, 511, 521 more effectively compared to the baseline receivers 810, 820, especially, for high-velocity or long delay profile scenarios. For this case the drop in throughput may be inevitable when switching to higher SCSs 501, 511, 521 assuming the same type of receiver 810, 820, 830. However, the same level of throughput as for the baseline receivers 810, 820 can be achieved with higher SCS 501, 511, 521 when using DeepRX 830. • For low load scenarios, the symbol duration 504 shrinks with switching to higher SCSs 501, 511, 521 and there will be no degradation on the throughput due to having time gaps 508 between consecutive symbols 506. • As DeepRx 830 is trained to operate under various different scenarios, parameters and configurations, it is more robust against the impairments in the received signal. As a result, DeepRX 830 outperforms the baseline receivers 810, 820 in case of having increased ISI induced by larger SCS 501, 511,521, and DeepRX 830 reduces the error caused by increasing the subcarrier spacing 501, 511, 521. FIG. 12 illustrates an example method 1200 according to examples of the disclosure. In some examples the method 1200 is performed by the network node 120. At block 1202, the network node 120 determines an adjustment of a subcarrier spacing 501, 511, 521 for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system. At block 1204, the network node 120 transmits to at least one user equipment 110 instructions 225, 455, 725, 765 to apply the adjustment to the subcarrier spacing 501, 511, 521 of the multi-carrier communications system. FIG. 13 illustrates an example method 1300 according to examples of the disclosure. In some examples the method 1300 is performed by the at least one user equipment 110. At block 1302, the user equipment 110 receives instructions 225, 455, 725, 765 to apply an adjustment to a subcarrier spacing 501, 511, 521 of a multi-carrier communications system, and apply an adjustment of time gaps 508 between symbols 506 in the multi-carrier communications system. At block 1304, the user equipment 110 adjusts the subcarrier spacing 501, 511, 521 of the multi-carrier communications system and adjusts time gaps 508 between symbols 506 in the multi-carrier communications system, in dependence upon the received instructions 225, 455, 725, 765. FIG. 14 illustrates an example of a controller 1400 suitable for use in an apparatus such as the user equipment 110 or the network node 120. Implementation of a controller 1400 may be as controller circuitry. The controller 1400 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in FIG. 14 the controller 1400 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1406 in a general-purpose or special-purpose processor 1402 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 1402. The processor 1402 is configured to read from and write to the memory 1404. The processor 1402 may also comprise an output interface via which data and / or commands are output by the processor 1402 and an input interface via which data and / or commands are input to the processor 1402. The memory 1404 stores a computer program 1406 comprising computer program instructions (computer program code) that controls the operation of the apparatus 110, 120 when loaded into the processor 1402. The computer program instructions, of the computer program 1406, provide the logic and routines that enables the apparatus to perform the methods illustrated in the accompanying Figs. The processor 1402 by reading the memory 1404 is able to load and execute the computer program 1406. The apparatus 120 comprises: at least one processor 1402; and at least one memory 1404 including computer program code the at least one memory 1404 and the computer program code configured to, with the at least one processor 1402, cause the apparatus 120 at least to perform: determining an adjustment of a subcarrier spacing 501, 511, 521 for a multicarrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and transmitting to at least one user equipment 110 instructions 225, 455, 725, 765 to apply the adjustment to the subcarrier spacing 501, 511, 521 of the multi-carrier communications system. The apparatus 110 comprises: at least one processor 1402; and at least one memory 1404 including computer program code the at least one memory 1404 and the computer program code configured to, with the at least one processor 1402, cause the apparatus 110 at least to perform: receiving instructions 225, 455, 725, 765 to apply an adjustment to a subcarrier spacing 501, 511, 521 of a multi-carrier communications system, and apply an adjustment of time gaps 508 between symbols 506 in the multi-carrier communications system; and adjusting the subcarrier spacing 501, 511, 521 of the multi-carrier communications system and adjusting time gaps 508 between symbols 506 in the multi-carrier communications system, in dependence upon the received instructions 225, 455, 725, 765. The apparatus 120 comprises: at least one processor 1402; and at least one memory 1404 storing instructions that, when executed by the at least one processor 1402, cause the apparatus at least to: determine an adjustment of a subcarrier spacing 501, 511, 521 for a multicarrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and transmit to at least one user equipment 110 instructions 225, 455, 725, 765 to apply the adjustment to the subcarrier spacing 501, 511, 521 of the multi-carrier communications system. The apparatus 110 comprises: at least one processor 1402; and at least one memory 1404 storing instructions that, when executed by the at least one processor 1402, cause the apparatus at least to: receive instructions 225, 455, 725, 765 to apply an adjustment to a subcarrier spacing 501, 511, 521 of a multi-carrier communications system, and apply an adjustment of time gaps 508 between symbols 506 in the multi-carrier communications system; and adjust the subcarrier spacing 501,511, 521 of the multi-carrier communications system and adjust time gaps 508 between symbols 506 in the multi-carrier communications system, in dependence upon the received instructions 225, 455, 725, 765. As illustrated in FIG. 15, the computer program 1406 may arrive at the apparatus 110, 120 via any suitable delivery mechanism 1408. The delivery mechanism 1408 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 1406. The delivery mechanism may be a signal configured to reliably transfer the computer program 1406. The apparatus 110, 120 may propagate or transmit the computer program 1406 as a computer data signal. Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: determining an adjustment of a subcarrier spacing 501, 511, 521 for a multicarrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; and transmitting to at least one user equipment 110 instructions 225, 455, 725, 765 to apply the adjustment to the subcarrier spacing 501, 511, 521 of the multi-carrier communications system. Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: receiving instructions 225, 455, 725, 765 to apply an adjustment to a subcarrier spacing 501, 511, 521 of a multi-carrier communications system, and apply an adjustment of time gaps 508 between symbols 506 in the multi-carrier communications system; and adjusting the subcarrier spacing 501, 511, 521 of the multi-carrier communications system and adjusting time gaps 508 between symbols 506 in the multi-carrier communications system, in dependence upon the received instructions 225, 455, 725, 765. The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 1404 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage. Although the processor 1402 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 1402 may be a single core or multi-core processor. References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’etc. ora ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the computer program 1406. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted. Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. The systems, apparatus, methods and computer programs may use machine learning which can include statistical learning. Machine learning is a field of computer science that gives computers the ability to learn without being explicitly programmed. The computer learns from experience E with respect to some class of tasks T and performance measure P if its performance at tasks in T, as measured by P, improves with experience E. The computer can often learn from prior training data to make predictions on future data. Machine learning includes wholly or partially supervised learning and wholly or partially unsupervised learning. It may enable discrete outputs (for example classification, clustering) and continuous outputs (for example regression). Machine learning may for example be implemented using different approaches such as cost function minimization, artificial neural networks, support vector machines and Bayesian networks for example. Cost function minimization may, for example, be used in linear and polynomial regression and K-means clustering. Artificial neural networks, for example with one or more hidden layers, model complex relationship between input vectors and output vectors. Support vector machines may be used for supervised learning. A Bayesian network is a directed acyclic graph that represents the conditional independence of a number of random variables. The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services. The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”. In this description, the wording ‘connect, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., so as to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, "determine / determining" can include resolving, selecting, choosing, establishing, and the like. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

1. An apparatus comprising:means for determining an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; andmeans for transmitting to at least one user equipment instructions to apply the adjustment to the subcarrier spacing of the multi-carrier communications system.

2. The apparatus of claim 1, wherein the multi-carrier communications system comprises a communications channel, and applying the adjustment to the subcarrier spacing of the multi-carrier communications system comprises applying the adjustment to the subcarrier spacing of the communications channel.

3. The apparatus of claim 1 or 2, wherein the instructions to apply the adjustment to the subcarrier spacing of the multi-carrier communications system comprises instructions to apply an adjustment of time gaps between symbols.

4. The apparatus of claim 3, wherein adjusting time gaps, comprises adding or removing time gaps.

5. The apparatus of claim 3 or 4, wherein the time gaps and subcarrier spacing are adjusted so that a symbol rate remains substantially the same.

6. The apparatus of any of the preceding claims, wherein determining an adjustment of the subcarrier spacing is in dependence upon a comparison of the input bit rate and a physical layer bit rate of the multi-carrier communications system.

7. The apparatus of claim 6, wherein:if the input bit rate is within an error margin of the physical layer bit rate the subcarrier spacing is not adjusted;if the input bit rate is more than an error margin below the physical layer bit rate the subcarrier spacing is increased; andif the input bit rate is more than an error margin above the physical layer bit rate the subcarrier spacing is decreased.

8. The apparatus of claim 6 or 7, wherein the physical layer bit rate is based on a modulation order, an active number of subcarriers, and a symbol duration.

9. The apparatus of any of the preceding claims, wherein the multi-carrier communications system uses orthogonal frequency-division multiplexing, OFDM, to transfer information.

10. The apparatus of any of the preceding claims, wherein the instructions to apply the adjustment to the subcarrier spacing comprises instructions to the at least one user equipment to enter a load constrained energy saving mode and adjust the subcarrier spacing of the multi-carrier communications system used by the at least one user equipment.

11. The apparatus of claim 10, further comprising means for receiving from at least one user equipment a load-constrained energy saving request for the at least one user equipment to enter a load-constrained energy saving mode, wherein entering the load-constrained energy saving mode comprises adjusting the subcarrier spacing of a multicarrier communications system used by the at least one user equipment.

12. The apparatus of any of the preceding claims, wherein the instructions to apply the adjustment to the subcarrier spacing specify a new subcarrier spacing.

13. The apparatus of any of the preceding claims, further comprising means for receiving a first transmission from the at least one user equipment with a first subcarrier spacing, and means for receiving a second transmission from the at least one user equipment with a second subcarrier spacing; wherein the first transmission is received before transmitting the instructions, and the second transmission is received after transmitting the instructions.

14. The apparatus of any of the preceding claims, further comprising means for determining a second adjustment of the subcarrier spacing for a multi-carriercommunications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; andmeans for transmitting to the at least one user equipment instructions to apply the second adjustment to the subcarrier spacing of the multi-carrier communications system.

15. The apparatus of claim 14, wherein the instructions to apply the second adjustment to the subcarrier spacing of the multi-carrier communications system comprise instructions to the at least one user equipment to exit a load constrained energy saving mode and adjust the subcarrier spacing of the multi-carrier communications system.

16. The apparatus of any of the preceding claims, further comprising means for determining an adjustment of a transmission power, discontinuous reception (DRX) cycle, discontinuous transmission (DTX) cycle and / or guard band size in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; andmeans for transmitting to at least one user equipment instructions to apply the adjustment to a transmission power, discontinuous reception (DRX) cycle, discontinuous transmission (DTX) cycle and / or guard band size of the multi-carrier communications system.

17. The apparatus of any of the preceding claims, further comprising means for adjusting the subcarrier spacing of a multi-carrier communications system in dependence upon the received instructions.

18. The apparatus of any of the preceding claims, wherein the subcarrier spacing is a continuous variable.

19. The apparatus of any of the preceding claims, wherein the apparatus is a base station.

20. A user equipment comprising:means for receiving instructions to apply an adjustment to a subcarrier spacing of a multi-carrier communications system, and to apply an adjustment of time gaps between symbols in the multi-carrier communications system; andmeans for adjusting the subcarrier spacing of the multi-carrier communications system and for adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions.

21. The user equipment of claim 20, wherein the means for adjusting the subcarrier spacing and for adjusting the time gaps between symbols is configured to adjust time gaps and subcarrier spacing so that a symbol rate remains substantially the same.

22. A method comprising:determining an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; andtransmitting to at least one user equipment instructions to apply the adjustment to the subcarrier spacing of the multi-carrier communications system.

23. A computer program comprising program instructions for causing an apparatus to perform at least the following:determining an adjustment of a subcarrier spacing for a multi-carrier communications system in dependence upon a change of an input bit rate for transfer via the multi-carrier communications system; andtransmitting to at least one user equipment instructions to apply the adjustment to the subcarrier spacing of the multi-carrier communications system.

24. A method comprising:receiving instructions to apply an adjustment to a subcarrier spacing of a multicarrier communications system, and to apply an adjustment of time gaps between symbols in the multi-carrier communications system; andadjusting the subcarrier spacing of the multi-carrier communications system and adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions.

25. A computer program comprising program instructions for causing an apparatus to perform at least the following:receiving instructions to apply an adjustment to a subcarrier spacing of a multicarrier communications system, and to apply an adjustment of time gaps between 5 symbols in the multi-carrier communications system; andadjusting the subcarrier spacing of the multi-carrier communications system and adjusting time gaps between symbols in the multi-carrier communications system, in dependence upon the received instructions.

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